Richard A. Isaacson Award in Gravitational-Wave Science

This award recognizes outstanding contributions in gravitational-wave physics, gravitational-wave astrophysics, and the technologies that enable this science.

The annual award consists of $5,000, a certificate, travel reimbursement and a registration waiver to attend the APS April Meeting to give an invited talk and accept the award.

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Biggish bang Artist's impression of neutron stars merging, producing gravitational waves and resulting in a kilonova explosion. (Courtesy: University of Warwick/Mark Garlick/CC BY 4.0)

05 Apr 2022

A massive and exotic type of neutron star could be formed by the merger of two neutron stars and avoid becoming a black hole – at least temporarily. That is the conclusion of Arthur Suvorov at Manly Astrophysics in Australia and Kostas Glampedakis at Germany’s University of Tübingen who have calculated that magnetically supramassive neutron stars could stave off gravitational collapse, despite lying above the theoretical mass limit for black hole formation.

In 2017 the LIGO–Virgo collaboration detected the first gravitational waves emanating from two neutron stars as they spiralled into each other, and eventually merged. This event provided important opportunities for astronomers to study the aftermath of the merger using a range of different telescopes, but key questions remain about the object that was created.

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Space.com

NEWS RELEASE 7-APR-2022

AMERICAN PHYSICAL SOCIETY

In the last seven years, scientists at the LIGO-Virgo Collaboration (LVC) have detected 90 gravitational waves signals. Gravitational waves are perturbations in the fabric of spacetime that race outwards from cataclysmic events like the merger of binary black holes (BBH). In observations from the first half of the most recent experimental run, which continued for six months in 2019, the collaboration reported signals from 44 BBH events.

But outliers were hiding in the data. Expanding the search, an international group of astrophysicists re-examined the data and found 10 additional black hole mergers, all outside the detection threshold of the LVC’s original analysis. The new mergers hint at exotic astrophysical scenarios that, for now, are only possible to study using gravitational wave astronomy.

“With gravitational waves, we’re now starting to observe the wide variety of black holes that have merged over the last few billion years,” says Physicist Seth Olsen, a Ph.D. candidate at Princeton University who led the new analysis. Every observation contributes to our understanding of how black holes form and evolve, he says, and the key to recognizing them is to find efficient ways to separate the signals from the noise.

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14 April 2022

The Dutch government intends to conditionally allocate 42 million euros from the Dutch National Growth Fund to the Einstein Telescope, and is also reserving 870 million euros for a future Dutch contribution to the construction. This decision was taken by the Cabinet based on the advice of the Advisory Committee of the National Growth Fund. With this decision, the Cabinet gives an enormous boost to Dutch science and to the broad development of the South Limburg border region.

The intended investment of 42 million euros will go towards preparatory work such as innovation of the necessary technology, location research, building up a high-tech ecosystem and organisation. With the reservation of the 870 million, the Netherlands has an excellent basis to apply in the future, together with Belgium and Germany, for the realisation of the Einstein Telescope in the border region of South Limburg.

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Supermassive black holes orbiting each other very closely are expected to produce gravitational waves.Credit: NASA’s Goddard Space Flight Center/Science Photo Library

Davide Castelvecchi -  Nature

27.1.2022

Astronomers could be on the verge of detecting gravitational waves from distant supermassive black holes — millions or even billions of times larger than the black holes spotted so far — an international collaboration suggests. The latest results from several research teams suggest they are closing in on a discovery after two decades of efforts to sense the ripples in space-time through their effects on pulsars, rapidly spinning spent stars that are sprinkled across the Milky Way.

Gravitational-wave hunters are looking for fluctuations in the signals from pulsars that would reveal how Earth bobs in a sea of gravitational waves. Like chaotic ripples in water, these waves could be due to the combined effects of perhaps hundreds of pairs of black holes, each lying at the centre of a distant galaxy.

So far, the International Pulsar Timing Array (IPTA) collaboration has found no conclusive evidence of these gravitational waves. But its latest analysis — using pooled data from collaborations based in North America, Europe and Australia — reveals a form of ‘red noise’ that has the features researchers expected to see. The findings were published on 19 January in Monthly Notices of the Royal Astronomical Society [1].

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Credit RIT

Matt Williams  - Universe Today

3.2.2022

In February 2016, scientists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) confirmed the first-ever detection of a gravitational wave event. Originally predicted by Einstein’s Theory of General Relativity, GWs result from mergers between massive objects – like black holes, neutron stars, and supermassive black holes (SMBHs). Since 2016, dozens of events have been confirmed, opening a new window to the Universe and leading to a revolution in astronomy and cosmology.

In another first, a team of scientists led by the Center for Computational Relativity and Gravitation (CCRG) announced that they may have detected a merger of two black holes with eccentric orbits for the first time. According to the team’s paper, which recently appeared in Nature Astronomy, this potential discovery could explain why some of the black hole mergers detected by the LIGO Scientific Collaboration and the Virgo Collaboration are much heavier than previously expected.

The team consisted of astrophysicists from the CCRG Rochester Institute of Technology, the Institute of Computational and Experimental Research in Mathematics (ICERM) at Brown University, and the University of Florida. As they indicate in their paper, the team took a fresh look at previous findings made in 2020, where they were part of the team that observed the most massive GW binary detected to date (GW190521). This consisted of two black holes that were about 85 and 66 Solar masses, respectively. This resulted in the formation of a black hole remnant of 142 solar masses.

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Collisions of two neutron stars (illustrated) probably produce more of the universe’s heavy elements than similar collisions of a black hole and neutron star. A. SIMONNET/SONOMA STATE UNIV., LIGO, NSF (EDITED BY MIT NEWS)

By Emily Conover NOVEMBER 3, 2021 

The cosmic origins of elements heavier than iron are mysterious. One elemental birthplace came to light in 2017 when two neutron-rich dead stars collided and spewed out gold, platinum and other hefty elements (SN: 10/16/17). A few years later, a smashup of another neutron star and a black hole left scientists wondering which type of cosmic clash was the more prolific element foundry (SN: 6/29/21).

Now, they have an answer. Collisions of two neutron stars probably take the cake, scientists report October 25 in Astrophysical Journal Letters.

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A black hole (illustrated in black) and a neutron star (white) spiral inward before merging, producing ripples in spacetime (dark gray). MARK MYERS/OZGRAV/SWINBURNE UNIVERSITY

An elusive source of ripples in spacetime has finally been found

By Emily Conover JUNE 29, 2021

Caught in a fatal inward spiral, a neutron star met its end when a black hole swallowed it whole. Gravitational ripples from that collision spread outward through the cosmos, eventually reaching Earth. The detection of those waves marks the first reported sighting of a black hole engulfing the dense remnant of dead star. And in a surprise twist, scientists spotted a second such merger just days after the first.

Until now, all identified sources of gravitational waves were twos of a kind: either two black holes or two neutron stars, spiraling around one another before colliding and coalescing (SN: 1/21/21). The violent cosmic collisions create waves that stretch and squeeze the fabric of spacetime, undulations that can be sussed out by sensitive detectors.

The mismatched pairing of a black hole and neutron star was the final type of merger that scientists expected to find with current gravitational wave observatories. By pure coincidence, researchers spotted two of these events within 10 days of one another, the LIGO, Virgo and KAGRA collaborations report in the July 1 Astrophysical Journal Letters.

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October 30, 2020• Physics 13, 164

The BICEP Array radio telescope, which searches for signatures of gravitational waves in the early Universe, has started an observing run that will break new ground in detection sensitivity.

In 2020, the raging pandemic halted many scientific endeavors around the globe. But after the last flights of the season left the Amundsen-Scott South Pole Station in February, the complex remained “frozen” in a pre-COVID era. There, a few dozen researchers can still mingle without face masks while managing physics, astronomy, and geoscience experiments that run during the six-month-long winter night. The latest experiment to kick off at the South Pole is the BICEP Array telescope, an instrument designed to probe the faint microwave light coming from the infant Universe. After a team assembled the new telescope in the brief austral summer, a lone engineer stayed to tend to the instrument (see Q&A: Searching for Light in the Darkness of Winter).

Focusing on a small patch of the South Pole’s dark winter sky, the BICEP Array will characterize with unprecedented accuracy the polarization of the cosmic microwave background (CMB). From these measurements, cosmologists hope to learn about inflation, the Universe’s extremely rapid expansion that occurred in the first 10−32
seconds after the big bang, before a more leisurely expansion began. They will examine subtle polarization patterns, called B modes, that theorists predict were produced by gravitational waves that arose during the inflation epoch.

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Daniel Meerburg  October 4, 2021• Physics 14, 135

An updated search for primordial gravitational waves has not found a signal, which implies that some popular early Universe models are becoming less viable.

Remarkably, the large-scale Universe can be adequately described by a model involving only a handful of parameters. This lambda cold dark matter (LCDM) model postulates that the expansion of the Universe is driven by the presence of two dark components—dark energy and dark matter—and that the galactic structure we observe today was sourced by small density variations in the very early Universe. However, cosmologists expect that these primordial density fluctuations were accompanied by fluctuations in the fabric of spacetime itself. These gravitational waves could be observed through a predicted signal in the cosmic microwave background (CMB). The BICEP/Keck Collaboration, which has been a frontrunner in the search for this illustrious signal, reports on its latest data set, finding no evidence of gravitational waves [1]. The resulting limits push up against model predictions, which suggests that we are either quickly closing in on a detection or that we may soon witness a paradigm shift. In addition, the analysis shows that researchers properly understand the astrophysical contaminants that obscure the search for this relic signature. By reducing uncertainties about this contamination, we should have greater confidence in any future claims of a detection.

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September 29, 2021

New mirror coatings will increase the volume of space LIGO can probe in its next run

Since LIGO's groundbreaking detection, in 2015, of gravitational waves produced by a pair of colliding black holes, the observatory, together with its European partner facility Virgo, has detected dozens of similar cosmic rumblings that send ripples through space and time.

In the future, as more and more upgrades are made to the National Science Foundation-funded LIGO observatories—one in Hanford, Washington, and the other in Livingston, Louisiana—the facilities are expected to detect increasingly large numbers of these extreme cosmic events. These observations will help solve fundamental mysteries about our universe, such as how black holes form and how the ingredients of our universe are manufactured.

One important factor in increasing the sensitivity of the observatories involves the coatings on the glass mirrors that lie at the heart of the instruments. Each 40-kilogram (88-pound) mirror (there are four in each detector at the two LIGO observatories) is coated with reflective materials that essentially turn the glass into mirrors. The mirrors reflect laser beams that are sensitive to passing gravitational waves.

Generally, the more reflective the mirrors the more sensitive the instrument, but there is a catch: The coatings that make the mirrors reflective also can lead to background noise in the instrument—noise that masks gravitational-wave signals of interest.

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Image from a MAYA collaboration numerical relativity simulation of a neutron star-black hole (NSBH) binary merger, showing the disruption of the neutron star. Credit: Deborah Ferguson (UT Ausitn), Bhavesh Khamesra (Georgia Tech), and Karan Jani (Vanderbilt University).

News Release • June 29, 2021

For the first time, researchers have confirmed the detection of a collision between a black hole and a neutron star. In fact, the scientists detected not one but two such events occurring just 10 days apart in January 2020. The extreme events made splashes in space that sent gravitational waves rippling across at least 900 million light-years to reach Earth. In each case, the neutron star was likely swallowed whole by its black hole partner.

Gravitational waves are disturbances in the curvature of space-time created by massive objects in motion. During the five years since the waves were first measured, a finding that led to the 2017 Nobel Prize in Physics, researchers have identified more than 50 gravitational-wave signals from the merging of pairs of black holes and of pairs of neutron stars. Both black holes and neutron stars are the corpses of massive stars, with black holes being even more massive than neutron stars.

Now, in a new study, scientists have announced the detection of gravitational waves from two rare events, each involving the collision of a black hole and a neutron star. The gravitational waves were detected by the National Science Foundation's (NSF's) Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and by the Virgo detector in Italy. The KAGRA detector in Japan, joined the LIGO-Virgo network in 2020, but was not online during these detections.

The first merger, detected on January 5, 2020, involved a black hole about 9 times the mass of our sun, or 9 solar masses, and a 1.9-solar-mass neutron star. The second merger was detected on January 15, and involved a 6-solar-mass black hole and a 1.5-solar-mass neutron star. The results were published today, June 29, in The Astrophysical Journal Letters.

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F. Elavsky and A. Geller/Northwestern Univ./LIGO-Virgo Collaboration

May 7, 2021• Physics 14, 67

The latest dataset from gravitational-wave observatories has enough events to allow researchers to study properties of the whole population of black holes.

Black holes (blue), neutron stars (orange), and compact objects of uncertain nature (gray) detected via gravitational waves through September 2019. Each binary merger involves three compact objects: the two coalescing objects and the final remnant. The vertical scale is in solar masses.

Less than six years after the first detection of gravitational waves, observations are becoming routine, with LIGO and Virgo logging black hole mergers more than once per week. At the APS April meeting, the LIGO-Virgo Collaboration (LVC) reported using their catalog of nearly 50 events to estimate the typical properties and histories of black holes. Measurements of black hole spins, for example, suggest that at least two different formation mechanisms are common for black hole binaries. These black hole “population” studies—akin to astronomers’ star surveys—are becoming a prized tool for gravitational-wave scientists, in addition to studies of individual events.

The black holes in the LVC catalog are stellar-mass black holes—the remnants of giant stars after they explode as supernovae. In the past, astronomers could spot these black holes only when they were in a binary orbit with a normal star, but the LIGO and Virgo observatories have revolutionized the field since 2015. “The vast majority of the stellar-mass black holes that we know about in the Universe [were detected via] gravitational waves,” said Carl Rodriguez of Carnegie Mellon University, Pennsylvania, in his presentation at the conference. So gravitational waves are now the main source of data from which astrophysicists will learn about these objects. “For the first time, we’re able to do astronomy” using gravitational waves, said Maya Fishbach of Northwestern University, Illinois, a member of the LVC. “We’re really going to learn more about star formation in general.”

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Europe’s proposed Einstein Telescope, an early design of which is shown here in an artist’s conception (not to scale), would comprise six detectors in a triangular arrangement of tunnels. ET CONCEPTUAL DESIGN TEAM

By Adrian Cho   Mar. 10, 2021

Just 5 years ago, physicists opened a new window on the universe when they first detected gravitational waves, ripples in space itself set off when massive black holes or neutron stars collide. Even as discoveries pour in, researchers are already planning bigger, more sensitive detectors. And a Ford versus Ferrari kind of rivalry has emerged, with scientists in the United States simply proposing bigger detectors, and researchers in Europe pursuing a more radical design.

“Right now, we’re only catching the rarest, loudest events, but there’s a whole lot more, murmuring through the universe,” says Jocelyn Read, an astrophysicist at California State University, Fullerton, who’s working on the U.S. effort. Physicists hope to have the new detectors running in the 2030s, which means they have to start planning now, says David Reitze, a physicist at the California Institute of Technology (Caltech). “Gravitational wave discoveries have captivated the world, so now is a great time to be thinking about what comes next.”

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Gravitational waves, produced when behemoths like black holes and neutron stars spiral inward and merge, have been spotted 50 times (each event represented with a large circle above). NADIEH BREMER/VISUALCINNAMON.COM

By Emily Conover and Nadieh Bremer

Fifty events reveal the similarities and differences in these cosmic smashups

Throughout the universe, violent collisions of cosmic beasts such as black holes wrench the fabric of spacetime, producing ripples called gravitational waves. For most of history, humans have been oblivious to those celestial rumbles. Today, we’ve detected scores of them.

The first came in 2015, when scientists with the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, spotted gravitational waves spawned from the merger of two black holes. That event rattled the bones of the cosmos — shaking the underlying structure of space and time. The detection also stirred up astronomy, providing a new way to observe the universe, and verified a prediction of Albert Einstein’s general theory of relativity (SN: 2/11/16).

The first came in 2015, when scientists with the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, spotted gravitational waves spawned from the merger of two black holes. That event rattled the bones of the cosmos — shaking the underlying structure of space and time. The detection also stirred up astronomy, providing a new way to observe the universe, and verified a prediction of Albert Einstein’s general theory of relativity (SN: 2/11/16).

But like a lone ripple in a vast sea, a single detection can tell scientists only so much. Now, LIGO and its partner observatory Advanced Virgo have collected 50 sets of gravitational waves. Most of these spacetime ripples resulted from two black holes spiraling inward before colliding. Some arose from collisions of dense stellar corpses called neutron stars. Two collisions involve celestial bodies that can’t be confidently identified, hinting that scientists may have spotted the first merger of a neutron star with a black hole (SN: 6/23/20).

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When neutron stars collide, the shell of expanding ejecta can interact with the surrounding interstellar medium, producing long-lived radio flaring. [NASA's Goddard Space Flight Center/CI Lab]

By Susanna Kohler on 11 December 2020

When a pair of neutron stars collide, they emit a fireworks show. Could some of the low-energy light produced in these mergers be detectable years later? A team of scientists thinks so — and they’re pretty sure they’ve found an example.

A Rainbow of Signals

In addition to gravitational waves, a slew of electromagnetic radiation is produced in the merger of two neutron stars, spanning the spectrum from gamma rays to radio waves.

In 2017, the now-famous neutron star collision GW170817 gave us a first look at this expected emission: it revealed a short gamma-ray burst, infrared and optical light from ejecta in a kilonova, and relatively short-lived X-ray and radio afterglows caused by high-speed outflows.

But there’s one expected type of emission that was missing from GW170817, and it’s never before been spotted in any neutron star collision: radio flaring.

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This illustration generated by a computer model shows multiple black holes found within the heart of a dense globular star cluster. Credit: Aaron M. Geller, Northwestern University/CIERA

New analysis of gravitational-wave data leads to wealth of discoveries.

An international research collaboration including Northwestern University astronomers has produced the most detailed family portrait of black holes to date, offering new clues as to how black holes form. An intense analysis of the most recent gravitational-wave data available led to the rich portrait as well as multiple tests of Einstein’s theory of general relativity. (The theory passed each test.)

The team of scientists who make up the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration is now sharing the full details of its discoveries. This includes new gravitational-wave detection candidates which held up to scrutiny — a whopping total of 39, representing a variety of black holes and neutron stars — and new discoveries as a result of combining all the observations. The 39 events averaged more than one per week of observing.

The observations could be a key piece in solving the many mysteries of exactly how binary stars interact. A better understanding of how binary stars evolve has consequences across astronomy, from exoplanets to galaxy formation.

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Scientists have now detected 50 sets of gravitational waves, many produced when two black holes (illustrated) spiral around one another before colliding and merging into one.
© N. FISCHER, S. OSSOKINE, H. PFEIFFER, A. BUONANNO/MAX PLANCK INSTITUTE FOR GRAVITATIONAL PHYSICS, SIMULATING EXTREME SPACETIMES (SXS) COLLABORATION

By Emily Conover OCTOBER 28, 2020 

Earth is awash in gravitational waves.

Over a six-month period, scientists captured a bounty of 39 sets of gravitational waves. The waves, which stretch and squeeze the fabric of spacetime, were caused by violent events such as the melding of two black holes into one.

The haul was reported by scientists with the LIGO and Virgo experiments in several studies posted October 28 on a collaboration website and at arXiv.org. The addition brings the tally of known gravitational wave events to 50.

The bevy of data, which includes sightings from April to October 2019, suggests that scientists’ gravitational wave–spotting skills have leveled up. Before this round of searching, only 11 events had been detected in the years since the effort began in 2015. Improvements to the detectors — two that make up the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, in the United States, and another, Virgo, in Italy — have dramatically boosted the rate of gravitational wave sightings.

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Impression of the Einstein Telescope, a large underground gravitational wave detector. As possible locations the Euro Region near Vaals and Sardinia are considered. IMAGE Nikhef / Thijs Balder

10 September 2020

Supported by the Netherlands, Belgium, Poland and Spain, the Italian government submitted an application on Wednesday to include the Einstein Telescope in a European roadmap for major research infrastructures. The inclusion of the Einstein Telescope in this ESFRI roadmap will be a recognition of the importance of the Einstein Telescope for Europe.

According to advanced plans, the Einstein Telescope will be the largest ever observatory for observing gravitational waves coming from colliding stars and black holes in the Universe. Such observations offer a new window on the cosmos and its history.

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An artist's impression of the last moments before the merger of two black holes. Credit: LIGO-VIRGO COLLABORATION

Jonathan Amos  -- BBC Science Correspondent
2 September 2020

Imagine the energy of eight Suns released in an instant.

This is the gravitational "shockwave" that spread out from the biggest merger yet observed between two black holes.
The signal from this event travelled for some seven billion years to reach Earth but was still sufficiently strong to rattle laser detectors in the US and Italy in May last year.
Researchers say the colliding black holes produced a single entity with a mass 142 times that of our Sun.
This is noteworthy. Science has long traced the presence of black holes on the sky that are quite a bit smaller or even very much larger. But this new observation inaugurates a novel class of so-called intermediate-sized black holes in the range of 100-1,000 Sun (or solar) masses.
The analysis is the latest to come out of the international LIGO-VIRGO collaboration, which operates three super-sensitive gravitational wave-detection systems in America and Europe.

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The link for the article in PRL 

© Carl Knox, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)

23 June 2020

Scientists puzzle over the mysterious astrophysical object: have they discovered the heaviest neutron star or the lightest black hole ever observed?

An international team of scientists including Lancaster University have discovered a compact object lying between neutron stars and black holes in terms of mass.

When the most massive stars die, they collapse under their own gravity and leave behind black holes; when stars that are a bit less massive die, they explode in a supernova and leave behind dense, dead remnants of stars called neutron stars.

For decades, astronomers have been puzzled by a gap that lies between neutron stars and black holes: the heaviest known neutron star is no more than 2.5 times the mass of our sun, or 2.5 solar masses, and the lightest known black hole is about 5 solar masses.

The question remained: does anything lie in this so-called mass gap?

Now, in a new study from the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector in Europe, scientists have announced the discovery of an object of 2.6 solar masses, placing it firmly in the mass gap.

The object was found on August 14, 2019, as it merged with a black hole of 23 solar masses, generating a splash of gravitational waves detected back on Earth by LIGO and Virgo. A paper about the detection has been accepted for publication in The Astrophysical Journal Letters.

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See the same news from Virgo website

See the same news from LIGO website

Marek Abramowicz, Michał Bejger, Éric Gourgoulhon & Odele Straub

Our existence in the Universe resulted from a rare combination of circumstances. The same must hold for any highly developed extraterrestrial civilisation, and if they have ever existed in the Milky Way, they would likely be scattered over large distances in space and time. However, all technologically advanced species must be aware of the unique property of the galactic centre: it hosts Sagittarius A* (Sgr A*), the closest supermassive black hole to anyone in the Galaxy. A civilisation with sufficient technical know-how may have placed material in orbit around Sgr A* for research, energy extraction, and communication purposes. In either case, its orbital motion will necessarily be a source of gravitational waves. We show that a Jupiter-mass probe on the retrograde innermost stable circular orbit around Sgr A* emits, depending on the black hole spin, at a frequency of fGW = 0.63–1.07 mHz and with a power of PGW = 2.7 × 10^36–2.0 × 10^37 erg/s. We discuss that the energy output of a single star is sufficient to stabilise the location of an orbiting probe for a billion years against gravitational wave induced orbital decay. Placing and sustaining a device near Sgr A* is therefore astrophysically possible. Such a probe will emit an unambiguously artificial continuous gravitational wave signal that is observable with LISA-type detectors.

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A visualization of a collision between two differently sized black holes.

Credit: N. Fischer, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics), Simulating eXtreme Spacetimes (SXS) Collaboration

Davide Castelvecchi,  20 APRIL 2020

Gravitational-wave astronomers have for the first time detected a collision between two black holes of substantially different masses — opening up a new vista on astrophysics and on the physics of gravity. The event offers the first unmistakable evidence from these faint space-time ripples that at least one black hole was spinning before merging, giving astronomers rare insight into a key property of these these dark objects.

“It’s an exceptional event,” said Maya Fishbach, an astrophysicist at the University of Chicago in Illinois. Similar mergers on which data have been published all took place between black holes with roughly equal masses, so this new one dramatically upsets that pattern, she says. The collision was detected last year, and was unveiled on 18 April by Fishbach and her collaborators at a virtual meeting of the American Physical Society, held entirely online because of the coronavirus pandemic.

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This simulation shows the radiation emitted from a binary black hole system. In principle, we should have neutron star binaries, black hole binaries, and neutron star-black hole systems, covering the entire allowable mass range. In practice, we saw a longstanding 'gap' in such binaries between about 2.5 and 5 solar masses. With the newest LIGO data, that gap seems to disappear.NASA'S GODDARD SPACE FLIGHT CENTER

Ethan Siegel

Mar 20, 2020

On Monday, March 16, 2020, astrophysicist Carl Rodriguez expressed a sentiment echoed by gravitational wave physicists all across the world: NOT NOW LIGO! Just minutes earlier, the LIGO collaboration sent out an alert suggesting that it had just detected another gravitational wave event, the 56th candidate detection since starting up its latest data-taking run in April of 2019. This one appears to indicate the merger of two black holes, like so many others before it.

Unlike most of the others, however, this one might be the nail-in-the-coffin of the idea of a "mass gap" between neutron stars and black holes. Before LIGO turned back on last April, all of its events, combined with otherwise-known neutron stars and black holes, showed two distinct populations: low-mass neutron stars (below 2.5 solar masses) and high-mass black holes (5 solar masses and up). This latest event, however, falls right into the mass gap range, and could demolish the idea once and for all.

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An artist's illustration of two black holes merging and creating ripples in spacetime known as gravitational waves.  (Image: © LIGO/T. Pyle)

By Paul Sutter 6.12.2019

Scientists are on the verge of being able to detect the "memory" left behind by gravitational waves.

Paul M. Sutter is an astrophysicist at The Ohio State University, host of Ask a Spaceman and Space Radio, and author of "Your Place in the Universe." Sutter contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

Gravitational waves slosh throughout the universe as ripples in space-time produced by some of the most cataclysmic events possible.

With facilities like the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo, we can now detect the strongest of those ripples as they wash over the Earth. But gravitational waves leave behind a memory — a permanent bend in space-time — as they pass through, and we are now on the verge of being able to detect that too, allowing us to push our understanding of gravity to the limits.

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NASA’S GODDARD SPACE FLIGHT CENTER/CI LAB

Astronomers still hope to catch a star going supernova and a bumpy neutron star, among others
BY LISA GROSSMAN 1:14PM, MAY 6, 2019

BANG, CRASH Physicists using the LIGO and Virgo observatories are catching all sorts of cosmic collisions, including of pairs of neutron stars (illustrated). But scientists hope to bag even more exotic quarry.

Seekers of gravitational waves are on a cosmic scavenger hunt.

Since the Advanced Laser Interferometer Gravitational-wave Observatory turned on in 2015, physicists have caught these ripples in spacetime from several exotic gravitational beasts — and scientists want more.

This week, LIGO and its partner observatory Virgo announced five new possible gravitational wave detections in a single month, making what was once a decades-long goal almost commonplace (SN Online: 5/2/19).

“We’re just beginning to see the field of gravitational wave astronomy open,” LIGO spokesperson Patrick Brady from the University of Wisconsin–Milwaukee said May 2 in a news conference. “Opening up a new window on the universe like this will hopefully bring us a whole new perspective on what’s out there.”

The speed and pitch of gravitational wave signals allow astronomers to make out what’s stirring up the waves. Here are the sources of gravitational waves that scientists that already have in their nets, and what they’re still hoping to find.

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Scientific simulation of a black hole consuming a neutron star.Credit: A. Tonita, L. Rezzolla, F. Pannarale

NATURE 26 APRIL 2019

Davide Castelvecchi

Gravitational waves may have just delivered the first sighting of a black hole devouring a neutron star. If confirmed, it would be the first evidence of the existence of such binary systems. The news comes just a day after astronomers had detected gravitational waves from a merger of two neutron stars for only the second time.

At 15:22:17 UTC on 26 April, the twin detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) in the United States and the Virgo observatory in Italy reported a burst of waves of an unusual type. Astronomers are still analysing the data and doing computer simulations to interpret them.

But they are already considering the tantalizing prospect that they have made a long-hoped-for detection that could produce a wealth of cosmic information, from precise tests of the general theory of relativity to measuring the Universe’s rate of expansion. Astronomers around the world are also racing to observe the phenomenon using different types of telescope.

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Scientific simulation of a black hole consuming a neutron star.Credit: A. Tonita, L. Rezzolla, F. Pannarale

NATURE 26 APRIL 2019

Davide Castelvecchi

Gravitational waves may have just delivered the first sighting of a black hole devouring a neutron star. If confirmed, it would be the first evidence of the existence of such binary systems. The news comes just a day after astronomers had detected gravitational waves from a merger of two neutron stars for only the second time.

At 15:22:17 UTC on 26 April, the twin detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) in the United States and the Virgo observatory in Italy reported a burst of waves of an unusual type. Astronomers are still analysing the data and doing computer simulations to interpret them.

But they are already considering the tantalizing prospect that they have made a long-hoped-for detection that could produce a wealth of cosmic information, from precise tests of the general theory of relativity to measuring the Universe’s rate of expansion. Astronomers around the world are also racing to observe the phenomenon using different types of telescope.

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Mollweide projection of bayestar.fits bayestar.png. Submitted by LIGO/Virgo EM Follow-Up on Apr 8, 2019 18:52:21 UTC

A week into the 3rd @LIGO @ego_virgo Observing Run and our first candidate has been posted to GraceDB - the #GravitationalWave candidate event database: say hello to S190408an! More info, including a map of its likely sky location, at https://gracedb.ligo.org/superevents/S190408an/view/ …

Stay tuned this week for more about our #GravitationalWave candidate events: how often to expect them, how to access the alert info and what it means. And remember, we're expecting *lots* of #O3 events and the alerts will be public! https://emfollow.docs.ligo.org/userguide/

GraceDB — Gravitational Wave Candidate Event Database

The Virgo gravitational-wave detector near Pisa, Italy, has roughly doubled its sensitivity since 2017.Credit: Cappello/Ropi via ZUMA

Detailed data on space-time ripples are set to pour in from LIGO and Virgo’s upgraded detectors.

Davide Castelvecchi  --  02 APRIL 2019

The hunt for gravitational waves is on again — this time assisted by the quirks of quantum mechanics.

Three massive detectors — the two in the United States called LIGO and one in Italy known as Virgo — officially resumed collecting data on 1 April, after a 19-month shutdown for upgrades. Thanks in part to a quantum phenomenon known as light squeezing, the machines promise not only to spot more gravitational waves — ripples in space-time that can reveal a wealth of information about the cosmos — but also to make more detailed detections. Researchers hope to observe as-yet undetected events, such as a supernova or the merging of a black hole with a neutron star.

The run, which will last until next March, also marks a major change in how gravitational-wave astronomy is done. For the first time, LIGO and Virgo will send out public, real-time alerts on wave detections to tip off other observatories — and anyone with a telescope — on how to find the events, so that they can be studied with traditional techniques, from radio- to space-based X-ray telescopes. The alerts will also be available through a smartphone app. “Astronomers are really hungry,” says David Reitze, a physicist at the California Institute of Technology in Pasadena and director of the Laser Interferometer Gravitational-wave Observatory (LIGO), which made the first historic detection of gravitational waves in 2015.

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A worker inspects quartz fibers that suspend a mirror inside the Virgo gravitational-wave observatory. EGO/Virgo Collaboration/Perciballi

Business Insider

Dave Mosher Mar. 28, 2019

One of the most remarkable experiments in history — a pair of giant machines that listen for ripples in spacetime called gravitational waves— will wake up from a half-year nap on Monday. And it will be about 40% stronger than before.

That experiment is called the Laser Interferometer Gravitational-Wave Observatory (LIGO); it consists of two giant, L-shaped detectors that together solved a 100-year-old mystery posed by Albert Einstein.

In 1915, Einstein predicted the existence of ripples in the fabric of space However, he didn't think these gravitational waves would ever be detected — they seemed too weak to pick up amid all the noise and vibrations on Earth. For 100 years, it seemed Einstein was right.

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Any distant gravitational source can emit gravitational waves and send out a signal that deforms the fabric of space, which manifests as gravitational attraction. But while gravitational forces fall off as the distance squared, the gravitational wave signal only falls off proportionally to the distance.

EUROPEAN GRAVITATIONAL OBSERVATORY, LIONEL BRET/EUROLIOS

Ethan Siegel - Senior Contributor
Mar 2, 2019

One of the things we often just accept about the world is that physical effects get weaker the farther away we get from them. Light sources appear dimmer, the gravitational force gets weaker, magnets deflect by smaller amounts, etc. The most common way this arises is through an inverse-square law, meaning that if you double the distance between you and the source that creates the effect you're measuring, the effect will be one quarter of what it was previously. But this isn't true for gravitational waves, and that puzzles reader Jack Dectis, who asks:

You have stated:
1) The strength of gravity varies with the square of the distance.
2) The strength of gravity waves, as detected by LIGO, varies directly with the distance.
So the question is, how can those two be the same thing?

This is a real surprise to almost everyone when they hear about it, even professional physicists. But it's true! Here's the science of why.

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A still image of a visualization of the merging black holes that LIGO and Virgo have observed so far. As the horizons of the black holes spiral together and merge, the emitted gravitational waves become louder (larger amplitude) and higher pitched (higher in frequency). The black holes that merge range from 7.6 solar masses up to 50.6 solar masses, with about 5% of the total mass lost during each merger.TERESITA RAMIREZ/GEOFFREY LOVELACE/SXS COLLABORATION/LIGO-VIRGO COLLABORATION

Dec 4, 2018,
Ethan Siegel Senior Contributor
Science

On September 14th, 2015, just days after LIGO first turned on at its new-and-improved sensitivity, a gravitational wave passed through Earth. Like the billions of similar waves that had passed through Earth over the course of its history, this one was generated by an inspiral, merger, and collision of two massive, ultra-distant objects from far beyond our own galaxy. From over a billion light years away, two massive black holes had coalesced, and the signal — moving at the speed of light — finally reached Earth.

But this time, we were ready. The twin LIGO detectors saw their arms expand-and-contract by a subatomic amount, but that was enough for the laser light to shift and produce a telltale change in an interference pattern. For the first time, we had detected a gravitational wave. Three years later, we've detected 11 of them, with 10 coming from black holes. Here's what we've learned.

There have been two "runs" of LIGO data: a first one from September 12, 2015 to January 19, 2016 and then a second one, at somewhat improved sensitivity, from November 30, 2016 to August 25, 2017. That latter run was, partway through, joined by the VIRGO detector in Italy, which added not only a third detector, but significantly improved our ability to pinpoint the location of where these gravitational waves occurred. LIGO is currently shut down right now, as it's undergoing upgrades that will make it even more sensitive, as it prepares to begin a new data-taking observing run in the spring of 2019.

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The Einstein Telescope, the European vision for a third-generation gravitational-wave detector, would consist of three interferometers formed into a triangle, with 10-kilometer-long arms. To minimize noise, it would be underground and cooled to around 10 K.

PHYSICS TODAY  - 01 OCTOBER 2018

Physics Today 71, 10, 25 (2018); https://doi.org/10.1063/PT.3.4041

Toni Feder

The promise of multimessenger astronomy drives the field, brings together scientific communities.

Word traveled fast when gravitational-wave detectors in the US and Europe announced the detection of a binary black hole merger on 14 September 2015. Then on 17 August 2017 the detection of merging neutron stars marked the beginning of multimessenger cosmic science with gravitational waves. (See Physics Today, April 2016, page 14, and December 2017, page 19.) Once that alert went out, dozens of telescopes were pointed toward the merger; radio astronomers are still watching it. Hundreds of papers followed, including one with more than 3500 authors. The excitement created by those detections has the gravitational-wave community chomping at the bit to lay plans for more powerful observatories.

Scientists in Europe put forward a design for the Einstein Telescope in 2011. (See Physics Today, September 2015, page 20.) Their US counterparts held off because NSF, which funded the bulk of the Laser Interferometer Gravitational-Wave Observatory (LIGO), encouraged them to score a detection before focusing on future observatories. So the US Cosmic Explorer design is less far along. But both future facilities would seek to increase sensitivity by at least a factor of 10.

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Artist's impression of a neutron-star merger (Courtesy: NASA)

Physics World

05 Sep 2018

A jet of charged particles moving at nearly the speed of light smashed its way out of debris left behind in the aftermath of the neutron-star merger that produced the gravitational waves detected by the LIGO–Virgo collaboration on 17 August 2017.

The event, catalogued as GW170817, has been a Rosetta Stone for astronomers because it allowed them for to observe the same event using gravitational waves and electromagnetic radiation ranging from a gamma ray burst (GRB) to a radio afterglow. This was a first for the new and exciting field of multimessenger astronomy.

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[Credit: NSF/LIGO/Sonoma State University/A. Simonnet]

B. F. Schutz
Posted on August 20, 2018

Last Friday we celebrated the one-year anniversary of an event that those of us who were involved will never forget. The Virgo gravitational-wave detector had joined the two LIGO instruments on August 1, 2017, and the three detectors had since then been patiently listening out together for gravitational wave sounds coming from anywhere in the Universe. On August 17, the deep quiet was interrupted by a squeal, a chirp lasting much longer and going to a much higher pitch than the GW150914 chirp that had launched the field of gravitational wave observational astronomy two years earlier. We named it, prosaically, GW170817.

This one-minute-long squeal was followed by an incredible explosion that radiated intense gamma-rays, X-rays, light, radio waves — right across the whole electromagnetic spectrum. What came first was a burst of gamma-rays, just 2 seconds after the end of the squeal. Then it began brightening up at other wavelengths. The explosion itself did not register in LIGO and Virgo, because as it rushed out in all directions it was too smooth to generate gravitational waves. But astronomers at their telescopes saw it: a kilonova, a new type of cosmic explosion.

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With the first detections behind them, researchers have set their sights on ambitious scientific quarry.

Davide Castelvecchi

In the mid-1980s, Bernard Schutz came up with a new solution to one of astronomy’s oldest problems: how to measure the distance from Earth to other objects in the cosmos. For generations, researchers have relied on an object’s brightness as a rough gauge for its distance. But this approach carries endless complications. Dim, nearby stars, for example, can masquerade as bright ones that are farther away.

Schutz, a physicist at the University of Cardiff, UK, realized that gravitational waves could provide the answer. If detectors could measure these ripples in space-time, emanating from interacting pairs of distant objects, scientists would have all the information needed to calculate how strong the signal was to start with — and so how far the waves must have travelled to reach Earth. Thus, he predicted, gravitational waves could be unambiguous markers of how quickly the Universe is expanding.

His idea was elegant but impractical: nobody at the time could detect gravitational waves. But, last August, Schutz finally got the opportunity to test this concept when the reverberations of a 130-million-year-old merger between two neutron stars passed through gravitational-wave detectors on Earth. As luck would have it, the event occurred in a relatively nearby galaxy, producing a much cleaner first measure than Schutz had dreamed. With that one data point, Schutz was able to show that his technique could become one of the most reliable for measuring distance. “It was hard to believe,” Schutz says. “But there it was.”

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Black holes in these environments could combine repeatedly to form objects bigger than anything a single star could produce.

Jennifer Chu | MIT News Office
April 10, 2018

When LIGO’s twin detectors first picked up faint wobbles in their respective, identical mirrors, the signal didn’t just provide first direct detection of gravitational waves — it also confirmed the existence of stellar binary black holes, which gave rise to the signal in the first place.
Stellar binary black holes are formed when two black holes, created out of the remnants of massive stars, begin to orbit each other. Eventually, the black holes merge in a spectacular collision that, according to Einstein’s theory of general relativity, should release a huge amount of energy in the form of gravitational waves.

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Article written: 10 Feb , 2016 Updated: 11 Feb , 2016

by Markus Pössel

It’s official: this Thursday, February 11, at 10:30 EST, there will be parallel press conferences at the National Press Club in Washington, D.C., in Hannover, Germany, and near Pisa in Italy. Not officially confirmed, but highly probable, is that people running the LIGO gravitational wave detectors will announce the first direct detection of a gravitational wave. The first direct detection of minute distortions of spacetime, travelling at the speed of light, first postulated by Albert Einstein almost exactly 100 years ago. Nobel prize time.

Time to brush up on your gravitational wave basics, if you haven’t done so! In Gravitational waves and how they distort space, I had a look at what gravitational waves do. Now, on to the next step: How can we measure what they do? How do gravitational wave detectors such as LIGO work?

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LISA Pathfinder performance analysis

5 February 2018

Imagine a packed party: music is blaring and you can feel the bass vibrate in your chest, lights are flashing, balloons are falling from the ceiling and the air is filled with hundreds of separate conversations. At the same time your cell phone is vibrating in your pocket and your drink is fizzing in the glass. Now imagine you can block out this assault on your senses to create a perfectly quiet bubble around you, only letting in the unmistakable voice of your best friend who’s trying to get your attention from the other side of the room.

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A simulation of a neutron star merger. NASA GODDARD SPACE FLIGHT CENTER

BY KATHERINE HIGNETT ON 1/19/18 AT 8:47 AM

Update | Last August, astronomers detected the massive collision of two neutron stars. This neutron star merger sent gravitational waves surging through space. It also unleashed a gamma ray burst—the world’s most powerful laser.

Normally gamma ray bursts glow brightly for a short time, then fizzle out and lose energy. New electromagnetic observations from NASA’s Chandra X-ray observatory show the burst brightening, baffling astronomers.

An exploding cocoon
A more complex explanation is needed for the bizarre brightening, the authors wrote. They propose that a "cocoon"-shaped explosion might do the job. In this model, a jet from the collision shock-heats the surrounding gas and debris, creating a boiling cocoon of matter.

The new X-ray observations support recent discoveries from radio emissions. Last month, another team of researchers reported the strengthening of radio emissions from the neutron star merger. They produced a digital reconstruction, seen in the video below, of a similar "cocoon" model.

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LISA has passed its Mission Definition Review with flying colours

January 22, 2018

Before an ESA mission reaches the launch pad, it has to go through a number of approval procedures that ensure the mission´s readiness. The future space-based gravitational wave observatory, the Laser Interferometer Space Antenna (LISA), has recently passed its Mission Definition Review (MDR) with flying colours.
The MDR's goal is to review and confirm that

• LISA's present mission design is feasible and suitable,
• the mission requirements meet LISA´s science requirements,
• the requirements are mature and adequate to the current phase,
• the technology developments are adequate to the current phase, and
• the interfaces between spacecraft, payload ground segment and launcher are well defined.

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In February of 2016, scientists working for the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first-ever detection of gravitational waves. Since that time, multiple detections have taken place, thanks in large to part to improvements in instruments and greater levels of collaboration between observatories. Looking ahead, its possible that missions not designed for this purpose could also “moonlight” as gravitational wave detectors.

For example, the Gaia spacecraft – which is busy creating the most detailed 3D map of the Milky Way – could also be instrumental when it comes to gravitational wave research. That’s what a team of astronomers from the University of Cambridge recently claimed. According to their study, the Gaia satellite has the necessary sensitivity to study ultra-low frequency gravitational waves that are produced by supermassive black hole mergers.

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Recent observations of a neutron star merger 130 million light years away found that gravitational waves and light from the event arrived at Earth within 2 s of one another. This indicates that the two fundamentally different types of wave travel at the same speed to within 1 part in 1015
. The finding constrains several theories that explain the accelerated expansion of the Universe using a modified version of general relativity in which gravity couples to a time-dependent scalar field, 𝜑(t)
. In such theories, the value of the scalar field needed to explain acceleration would lead to gravitational waves (orange) that travel at significantly different speeds from that of light (light blue) [2–5]. Show less

Fabian Schmidt, Max Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, Garching, 85748, Germany

December 18, 2017• Physics 10, 134

Theorists have tightly constrained alternative theories of gravity using the recent joint detection of gravitational waves and light from a neutron star merger.

Our current theory of gravity, general relativity (GR), has been spectacularly successful. It accurately describes the dynamics of astronomical objects over a vast range of sizes from planets and stars, to black holes, all the way to galaxies. GR also predicts the expansion of the Universe as a whole.

But the theory has fallen short in one respect: explaining the finding that the Universe is expanding at an accelerating rate. According to GR, the sum of all known radiation, visible matter, and dark matter should exert an inward “tug” on the Universe, slowing down its rate of expansion over time. So to account for acceleration, physicists have been forced to consider three possibilities [1], all of which are often loosely referred to as “dark energy.” The first option—and also the simplest and most favored—is the existence of a cosmological constant, or vacuum energy, which counteracts gravity by exerting a constant negative effective pressure. The second imagines that the cosmological constant is actually dynamical. Finally, the third possibility is that gravity behaves differently on large distance scales, requiring a modification of GR. Using the recent detection of a gravitational wave and light from a distant binary neutron merger, four research groups have now placed some of the tightest constraints to date on this third scenario [2–5].

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NSF, LIGO, SONOMA STATE UNIV., A. SIMONNET

CRASH AND WAVE In a galaxy 130 million light-years away, two neutron stars collided. This year, in the first detection of its kind, observatories caught the resulting gravitational waves and light show (illustrated).

Discovery offers clues to heavy element formation, universe’s expansion and more
BY EMILY CONOVER 8:31AM, DECEMBER 13, 2017

Thousands of astronomers and physicists. Hundreds of hours of telescope observations. Dozens of scientific papers. Two dead stars uniting into one.

In 2017, scientists went all in on a never-before-seen astronomical event of astounding proportions: a head-on collision between two neutron stars, the ultradense remnants of exploded stars.

The smashup sent shivers of gravitational waves through Earth, and the light show that followed sent shivers of excitement down astronomers’ spines. A real-life scientific drama quickly unfolded as night after night, astronomers around the world raced the sunrise, capturing every possible bit of data before day broke at their observatories.

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Copyright: F.PLAS/IHES/CNRS PHOTOTHEQUE

On December 14, 2017, Alain Brillet and Thibault Damour will receive the CNRS Gold Medal, France's highest scientific distinction, during a ceremony at the Collège de France in Paris. Together, the two scientists contributed decisively to the discovery of gravitational waves in 2015.

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Until recently, simulations of the universe haven’t given its lumps their due

BY EMILY CONOVER 3:30PM, NOVEMBER 14, 2017

Magazine issue: Vol. 192 No. 9, November 25, 2017, p. 22

If the universe were a soup, it would be more of a chunky minestrone than a silky-smooth tomato bisque.

Sprinkled with matter that clumps together due to the insatiable pull of gravity, the universe is a network of dense galaxy clusters and filaments — the hearty beans and vegetables of the cosmic stew. Meanwhile, relatively desolate pockets of the cosmos, known as voids, make up a thin, watery broth in between.

Until recently, simulations of the cosmos’s history haven’t given the lumps their due. The physics of those lumps is described by general relativity, Albert Einstein’s theory of gravity. But that theory’s equations are devilishly complicated to solve. To simulate how the universe’s clumps grow and change, scientists have fallen back on approximations, such as the simpler but less accurate theory of gravity devised by Isaac Newton.

Relying on such approximations, some physicists suggest, could be mucking with measurements, resulting in a not-quite-right inventory of the cosmos’s contents. A rogue band of physicists suggests that a proper accounting of the universe’s clumps could explain one of the deepest mysteries in physics: Why is the universe expanding at an increasingly rapid rate?

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News Release • November 15, 2017

Scientists searching for gravitational waves have confirmed yet another detection from their fruitful observing run earlier this year. Dubbed GW170608, the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun, at a distance of about a billion light-years from Earth. The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision.

This event, detected by the two NSF-supported LIGO detectors at 02:01:16 UTC on June 8, 2017 (or 10:01:16 pm on June 7 in US Eastern Daylight time), was actually the second binary black hole merger observed during LIGO’s second observation run since being upgraded in a program called Advanced LIGO. But its announcement was delayed due to the time required to understand two other discoveries: a LIGO-Virgo three-detector observation of gravitational waves from another binary black hole merger (GW170814) on August 14, and the first-ever detection of a binary neutron star merger (GW170817) in light and gravitational waves on August 17.

A paper describing the newly confirmed observation, “GW170608: Observation of a 19-solar-mass binary black hole coalescence,” authored by the LIGO Scientific Collaboration and the Virgo Collaboration has been submitted to The Astrophysical Journal Letters and is available to read on the arXiv. Additional information for the scientific and general public can be found at http://www.ligo.org/detections/GW170608.php.

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Natalie Wolchoverm --  October 25, 2017 

Newly discovered “standard sirens” provide an independent, clean way to measure how fast the universe is expanding.

To many cosmologists, the best thing about neutron-star mergers is that these events scream into space an otherwise close-kept secret of the universe. Scientists combined the gravitational and electromagnetic signals from the recently detected collision of two of these stars to determine, in a cleaner way than with other approaches, how fast the fabric of the universe is expanding — a much-contested number called the Hubble constant.

In the days since the neutron-star collision was announced, Hubble experts have been surprised to find themselves discussing not whether events like it could settle the controversy, but how soon they might do so.

Scientists have hotly debated the cosmic expansion rate ever since 1929, when the American astronomer Edwin Hubble first established that the universe is expanding - and that it therefore had a beginning. How fast it expands reflects what’s in it (since matter, dark energy and radiation push and pull in different ways) and how old it is, making the value of the Hubble constant crucial for understanding the rest of cosmology.

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NSF/Steffen Richter/Harvard Univ./SPL : Telescopes in Antarctica track the cosmic microwave background radiation left over from the Big Bang.

Multi-telescope project has ambitious goals and a big price tag.

Edwin Cartlidge - 30 October 2017

US researchers have drafted plans to study the faint afterglow of the Big Bang using a new facility. They hope it will be sensitive enough to confirm whether or not the infant Universe underwent a brief period of explosive expansion known as inflation.

The Cosmic Microwave Background Stage-4 experiment (CMB-S4) would comprise three 6-metre and 14 half-metre telescopes distributed across two sites in Antarctica and Chile, according to a preliminary design due to be made public this week. Potentially up and running within a decade, the facility would be nearly 100 times as sensitive as existing ground-based CMB experiments.

It won’t be cheap, however. Construction will cost a little over US$400 million, according to the expert task force commissioned by the US Department of Energy (DOE) and National Science Foundation (NSF) to produce the design. That is at least twice as much as envisioned in a less-detailed review 3 years ago, and 30 times the cost of existing experiments.

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The core of a neutron star is such an extreme environment that physicists can’t agree on what happens inside. But a new space-based experiment — and a few more colliding neutron stars — should reveal whether neutrons themselves break down.

Joshua Sokol - Contributing Writer - October 30, 2017

The alerts started in the early morning of Aug. 17. Gravitational waves produced by the wreck of two neutron stars — dense cores of dead stars — had washed over Earth. The thousand-plus physicists of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) rushed to decode the space-time vibrations that rolled across the detectors like a drawn-out peal of thunder. Thousands of astronomers scrambled to witness the afterglow. But officially, all this activity was kept secret. The data had to be collected and analyzed, the papers written. The outside world wouldn’t know for two more months.

The strict ban put Jocelyn Read and Katerina Chatziioannou, two members of the LIGO collaboration, in a bit of an awkward situation. In the afternoon on the 17th, the two were scheduled to lead a panel at a conference dedicated to the question of what happens under the almost unfathomable conditions in a neutron star’s interior. Their panel’s topic? What a neutron-star merger would look like. “We sort of went off at the coffee break and sat around just staring at each other,” said Read, a professor at California State University, Fullerton. “OK, how are we going to do this?”

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BANG, FLASH Light waves and gravitational waves from a pair of colliding neutron stars reached Earth at almost the same time, ruling out theories about the universe based on predictions that the two kinds of waves might travel at different speeds

Speed of spacetime ripples rules out some alternatives to dark energy
BY LISA GROSSMAN 5:34PM, OCTOBER 24, 2017

Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.

On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17). Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection. That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.

Within a day, five papers were posted at arXiv.org mourning hundreds of expanding universe theories that predicted gravitational waves should travel faster than light — an impossibility without changes to Einstein’s laws of gravity. These theories “are very, very dead,” says the coauthor of one of the papers, cosmologist Miguel Zumalacárregui of the Nordic Institute for Theoretical Physics, or NORDITA, in Stockholm. “We need to go back to our blackboards and start thinking of other alternatives.”

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A cloud of debris ejected into space as two neutron stars merge. (Credit: NASA Goddard Space Flight Center/CI Lab)

By Nathaniel Scharping | October 16, 2017

The first gravitational wave observed from a neutron star merger offers the potential for a whole raft of new discoveries. Among them is a more precise measurement of the Hubble constant, which captures how fast our universe is expanding.

Ever since the Big Bang, everything in the universe has been spreading apart. It also turns out that this is happening faster and faster — the rate of expansion is increasing.

We’ve known this for a century, but astronomers haven’t been able to get precise measurements of the increase in rate, due mostly to the fact that they’ve had to cobble together a range of data to estimate how far away things in the universe are. Gravitational wave observations offer a direct means of measuring distances in the universe. The LIGO collaboration is constantly monitoring the universe for the subtle stretching of space-time that huge astronomical collisions can create, and measurements of the amplitude and frequency of the waves it catches hold valuable information for astronomers.

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Artist’s impression of two neutron stars – the compact remnants of what were once massive stars – spiralling towards each other just before merging.

The collision of these dense, compact objects produced gravitational waves – fluctuations in the fabric of spacetime – that were detected by the LIGO/Virgo collaboration on 17 August 2017. A couple of seconds after that, ESA's Integral and NASA’s Fermi satellites detected a burst of gamma rays, the luminous counterpart to the gravitational waves emitted by the cosmic clash.

This is the first discovery of gravitational waves and light coming from the same source.

Full story

Zwei Neutronensterne verschmelzen und explodieren. Erstmals fingen Forscher ein solches Ereignis direkt ein. Und lösen Grundfragen der Astronomie. © ESO/L. Calçada/M. Kornmesser

Gerade den Nobelpreis eingesackt und nun das: Die Gravitationswellenjäger fangen das Echo einer Sternenexplosion ein und katapultieren die Astronomie in eine neue Ära.

Von Ulrich Schnabel  -- 16. Oktober 2017

Das Leben schreibt bekanntlich die besten Geschichten, und die Erforschung der Gravitationswellen gehört sicher zu den schönsten Storys der modernen Wissenschaft: Rund 100 Jahre lang blieben sie verborgen, wie Dornröschen hinter der Märchenhecke, und alle Nachweisversuche scheiterten. Dann wurden sie endlich entdeckt, verkündet fast auf den Tag genau 100 Jahre, nachdem Einstein sie postuliert hatte. Und seither geht es Schlag auf Schlag: Immer neue Gravitationswellenfunde wurden in den vergangenen Monaten vermeldet, gerade wurde ihr Nachweis mit dem Nobelpreis geehrt und nun das nächste große Ding: Weltweit jubeln Astronomen über einen ganz besonderen Fund, der gleich mehrere kosmische Rätsel auf einmal löst.

"Es kommt nur selten vor, dass ein Wissenschaftler Zeuge des Beginns einer neuen Ära werden kann", sagt die italienische Astronomin Elena Pian, eine der Entdeckerinnen. Doch der heute vorgestellte Fund sei genau ein solch historischer Moment. Ähnlich euphorisch klingen ihre Kollegen. "Wir befinden uns jetzt im Zeitalter der Multi-Messenger-Astronomie!" So triumphierend formuliert es der britische Astrophysiker Andrew Levan, Autor eines von insgesamt sieben (!) Fachartikeln, in denen die Entdeckung in den Zeitschriften Nature und Nature Astronomy ausgebreitet wird.

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By Ashley Strickland, CNN
Updated 2325 GMT (0725 HKT) October 16, 2017

(CNN)For the first time, two neutron stars in a nearby galaxy have been observed engaging in a spiral death dance around one another until they collided. What resulted from that collision is being called an "unprecedented" discovery that is ushering in a new era of astronomy, scientists announced Monday.

"We can now fill in a few more tiles in the jigsaw puzzle that is the story of our universe," said Laura Cadonati, deputy spokeswoman for the LIGO Scientific Collaboration and professor in the school of physics at Georgia Tech.
The collision created the first observed instance of a single source emitting ripples in space-time, known as gravitational waves, as well as light, which was released in the form of a two-second gamma ray burst. The collision also created heavy elements such as gold, platinum and lead, scattering them across the universe in a kilonova -- similar to a supernova -- after the initial fireball.

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An illustration of two neutron stars colliding. NASA

• For the first time, astronomers have detected a neutron-star collision.
• Gravitational waves heard by two detectors pinpointed the source to a galaxy 130 million light-years away.
• The collision produced a radioactive "kilonova" that forged hundreds of Earths' worth of platinum, gold, silver, and other atoms.
• The discovery solves a longstanding mystery about the origins of heavy elements.

Platinum and gold are among the most precious substances on Earth, each fetching roughly $1,000 an ounce.

However, their allure may grow stronger — and weirder — thanks to a groundbreaking new finding about their violent, radioactive, and cosmic origins.

On Monday, scientists who won a Nobel Prize for their discovery of gravitational waves, or ripples in the fabric of space, announced the first detection of the collision of two neutron stars.

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The fifth observation of gravitational waves (GW) marks the beginning of a new era in astronomy. On August 17, 2017, the LIGO and VIRGO collaborations detected neutron stars merging for the first time and immediately alerted observatories around the world. In a matter of hours the event had been located, another first for GW astronomy, and telescopes around the world begun studying it almost immediately.

The event observed, called GW170817, was produced in galaxy NGC 4993, located 130 million light-years from Earth. The gravitational signal was the strongest ever observed, lasting over 100 seconds, and it emitted a gamma-ray burst (GRBs), providing the first piece of evidence that GRBs are produced by neutron star collisions. It also provided the strongest evidence yet that neutron star mergers are responsible for the creation of the heaviest elements in the universe, like gold and platinum.

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For decades, researchers believed that violent supernovas forged gold and other heavy elements. But many now argue for a different cosmic quarry.

Across history and folklore, the question of where Earth’s gold came from — and maybe how to get more of it — has invited fantastical explanation. The Inca believed gold fell from the sky as either the tears or the sweat of the sun god Inti. Aristotle held that gold was hardened water, transformed when the sun’s rays penetrated deep underground. Isaac Newton transcribed a recipe for making it with a philosopher’s stone. Rumpelstiltskin, of course, could spin it from straw.

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 An artist’s rendering of the merger of two neutron stars from Aug. 17. Credit Robin Dienel/The Carnegie Institution for Science

Astronomers announced on Monday that they had seen and heard a pair of dead stars collide, giving them their first glimpse of the violent process by which most of the gold and silver in the universe was created.

The collision, known as a kilonova, rattled the galaxy in which it happened 130 million light-years from here in the southern constellation of Hydra, and sent fireworks across the universe. On Aug. 17, the event set off sensors in space and on Earth, as well as producing a loud chirp in antennas designed to study ripples in the cosmic fabric. It sent astronomers stampeding to their telescopes, in hopes of answering one of the long-sought mysteries of the universe.

LIGO Detects Fierce Collision of Neutron Stars for the First Time

By Nicolas Arnaud  -- October 11, 2017

*** MEDIA ADVISORY ***
Issued jointly by the LIGO Laboratory, LIGO Scientific Collaboration, National Science Foundation, and Virgo Collaboration

Scientists representing LIGO, Virgo, and some 70 observatories will reveal new details and discoveries made in the ongoing search for gravitational waves.

WHAT: Journalists are invited to join the National Science Foundation as it brings together scientists from the LIGO and Virgo collaborations, as well as representatives for some 70 observatories, on Monday, October 16, at 16:00 CEST at the National Press Club in Washington, D.C.

The gathering will begin with an overview of new findings from LIGO, Virgo, and partners that span the globe, followed by details from telescopes that work with the LIGO and Virgo Collaboration to study extreme events in the cosmos.

The first detection of gravitational waves, made on September 14, 2015 and announced on February 11, 2016, was a milestone in physics and astronomy; it confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity, and marked the beginning of the new field of gravitational-wave astronomy. Since then, there have been three more confirmed detections, one of which (and the most recently announced) was the first confirmed detection seen jointly by both the LIGO and Virgo detectors.

The published articles announcing LIGO-Virgo’s first, second, and third confirmed detections have been cited more than 1,700 times (total), according to the Web of Science citation counts. A fourth paper on the three-detector observation was published on October 6; a manuscript was made publicly available on September 27.

WHEN: Monday, October 16, 2017  16:00 CEST

** Panels to begin at 16:00 and 17:15, with a 15-minute break in between. Event expected to conclude by 18:30.

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ESO will hold a press conference on 16 October 2017 at 16:00 CEST, at its Headquarters in Garching, Germany, to present groundbreaking observations of an astronomical phenomenon that has never been witnessed before.

The event will be introduced from ESO’s Paranal Observatory in Chile by the Director General, Xavier Barcons, and will feature talks by representatives of many research groups around Europe.

This invitation is addressed exclusively at media representatives. To participate in the conference, bona fide members of the media must register by completing an online form. Please indicate whether you wish to come in person to the press conference or if you will participate online only.

By registering for the conference, journalists agree to honour an embargo, details of which will be provided after registration, and not to publish or discuss any of the material presented before the start of the conference on 16 October 2017 at 16:00 CEST.

On site journalists will have a question and answer session with panelists during the conference. We will also take questions from journalists participating online. In-person individual interviews right after the conference are also possible.

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Artist’s impression of a gamma-ray burst, a powerful flash of gamma-rays that may be emitted from the merger of a neutron star with another compact object. [ESO/A. Roquette]

By Susanna Kohler on 9 October 2017

With the first detection of gravitational waves in 2015, scientists celebrated the opening of a new window to the universe. But multi-messenger astronomy — astronomy based on detections of not just photons, but other signals as well — was not a new idea at the time: we had already detected tiny, lightweight neutrinos emitted from astrophysical sources. Will we be able to combine observations of neutrinos and gravitational waves in the future to provide a deeper picture of astrophysical events?

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Figure 1. John T. Tate, circa 1930. Tate edited the Physical Review at the University of Minnesota from 1926 until his death in 1950.

Daniel Kennefick Physics Today 58, 9, 43 (2005) [Comment by KK: it's worth reading]

Albert Einstein had two careers as a professional physicist, the first spent through 1933 entirely at German-speaking universities in central Europe, the second at the Institute for Advanced Studies in Princeton, New Jersey, from 1933 until his death in 1955. During the first period he generally published in German physics journals, most famously the Annalen der Physik, where all five of his celebrated papers of 1905 appeared.

After relocating to the US, Einstein began to publish frequently in North American journals. Of those, the Physical Review, then under the editorship of John Tate (pictured in figure 1), was rapidly assuming the mantle of the world’s premier journal of physics.  Einstein first published there in 1931 on the first of three winter visits to Caltech. With Nathan Rosen, his first American assistant, Einstein published two more papers in the Physical Review: the famous 1935 paper by Einstein, Boris Podolsky, and Rosen (EPR) and a 1936 paper that introduced the concept of the Einstein–Rosen bridge, nowadays better known as a wormhole. But except for a letter to the journal’s editor he wrote in 1952—in response to a paper critical of his unified field theory work—that 1936 paper was the last Einstein would ever publish there.

Einstein stopped submitting work to the Physical Review after receiving a negative critique from the journal in response to a paper he had written with Rosen on gravitational waves later in 1936. That much has long been known, at least to the editors of Einstein’s collected papers. But the story of Einstein’s subsequent interaction with the referee in that case is not well known to physicists outside of the gravitational-wave community. Last March, the journal’s current editor-in-chief, Martin Blume, and his colleagues uncovered the journal’s logbook records from the era, a find that has confirmed the suspicions about that referee’s identity.  Moreover, the story raises the possibility that Einstein’s gravitational-wave paper with Rosen may have been his only genuine encounter with anonymous peer review. Einstein, who reacted angrily to the referee report, would have been well advised to pay more attention to its criticisms, which proved to be valid.

DOUBTING GRAVITATIONAL WAVES

Einstein introduced gravitational waves into his theory of general relativity in 1916...

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Rainer Weiss                                                       Kip Thorne                                       Barry Barish

A recent study provides a renewed look at whether the universe's dark matter could be primordial black holes — and, if so, whether LIGO could detect them. [dark matter. [SXS Lensing]

By Susanna Kohler on 27 September 2017 

Today promises to be an exciting day in the world of gravitational-wave detections. To keep with the theme, we thought we’d use this opportunity to take a renewed look at an interesting question about the Laser Interferometer Gravitational-Wave Observatory (LIGO) and dark matter: if dark matter is made up of primordial black holes, will LIGO be able to detect them?

Black Holes in the Early Universe

The black holes we generally think about in the context of gravitational-wave detections are black holes formed by the collapse of massive stars. Indeed, LIGO’s detections have thus far been of merging black holes weighing between 7 and 35 solar masses — the perfect sizes to have formed from massive-star collapses.

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News Release • September 27, 2017

The LIGO Scientific Collaboration and the Virgo collaboration report the first joint detection of gravitational waves with both the LIGO and Virgo detectors. This is the fourth announced detection of a binary black hole system and the first significant gravitational-wave signal recorded by the Virgo detector, and highlights the scientific potential of a three-detector network of gravitational-wave detectors.

The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, and funded by the National Science Foundation (NSF), and the Virgo detector, located near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.

A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.

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See the paper

News Release • September 27, 2017

The LIGO Scientific Collaboration and the Virgo collaboration report the first joint detection of gravitational waves with both the LIGO and Virgo detectors. This is the fourth announced detection of a binary black hole system and the first significant gravitational-wave signal recorded by the Virgo detector, and highlights the scientific potential of a three-detector network of gravitational-wave detectors.

The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, and funded by the National Science Foundation (NSF), and the Virgo detector, located near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.

A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.

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Are we about to make a breakthrough to go beyond black holes? Here’s what it means if we do!

If there’s one major difference between General Relativity and Newtonian gravity, it’s this: in Einstein’s theory, nothing lasts forever. Even if you had two perfectly stable masses in orbit around one another — masses that never burned out, lost material, or otherwise changed — their orbits would eventually decay. Whereas in Newtonian gravity, two masses would orbit their mutual center of gravity for an eternity, relativity tells us that a tiny amount of energy gets lost with every moment that one mass is accelerated by the gravitational field it passes through. That energy doesn’t disappear, but gets carried away in the form of gravitational waves. Over long enough time periods, enough energy is radiated away that those two orbiting masses will touch and merge together. Three times, now, LIGO has seen this happen for black holes. But it may be about to take the next step, and see neutron stars merge for the first time.

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A still from a computer simulation of merging neutron stars, which are thought to power short gamma-ray bursts. Rumors are swirling that gravitational-wave observatories as well as electromagnetic ground- and space-based telescopes have all spied such a merger in the distant galaxy NGC 4993. Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla

Astrophysicists may have detected gravitational waves last week from the collision of two neutron stars in a distant galaxy—and telescopes trained on the same region might also have spotted the event.

Rumours to that effect are spreading fast online, much to researchers’ excitement. Such a detection could mark a new era of astronomy: one in which phenomena are both seen by traditional telescopes and ‘heard’ as vibrations in the fabric of space-time. “It would be an incredible advance in our understanding,” says Stuart Shapiro, an astrophysicist at the University of Illinois at Urbana-Champaign.

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A fundamental challenge
Bill Saxton/NRAO/AUI/NSF

By Joshua Sokol

Imagine you’re an astronomer with bright ideas about the hidden laws of the cosmos. Like any good scientist, you craft an experiment to test your hypothesis.

Then comes bad news – there’s no way to carry it out, except maybe in a computer simulation. For cosmic objects are way too unwieldy for us to grow them in Petri dishes or smash them together as we do with subatomic particles.

Thankfully, though, there are rare places in space where nature has thrown together experiments of its own – like PSR J0337+1715. First observed in 2012 and announced in 2014, this triple system is 4200 light years away in the constellation Taurus.

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The GEO600 gravitational-wave detector in Hanover, Germany, tests technologies that are deployed in larger gravitational-wave observatories such as LIGO.

Physicists find ways to make LIGO and other gravitational-wave detectors even more sensitive.

Elizabeth Gibney
12 July 2017

Gravitational-wave observatories have some of the most sensitive detectors on the planet, which allows them to spot the faint ripples in space-time that pass through Earth from the collisions of massive black holes billions of light years away. But their ability to catch more subtle signals is constrained by fundamental quantum limits. Now physicists are devising tricks to get around this problem. The goal is to peer farther into the Universe and to spot the effects of collisions between less massive objects, such as neutron stars.

The US-based Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) is already planning to use photonics techniques to ‘squeeze’ light. That should increase LIGO’s sensitivity by 50%. Quantum physicists from outside the gravitational-wave community are pitching in with new ideas, too. In Nature this week, they describe a technique that could, in theory, double the sensitivity of detectors (C. B. Møller et al. Nature 547, 191–195; 2017).

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(Image Credits: Chris Klimek)

Jun 27, 2017

by Panos Charitos

Kip Thorne is one of the leading physicists working on Einstein's theory of relativity today. He has pioneered the scientific investigation of black holes in the universe. He was one of the founders of the LIGO project to detect gravitational waves and he has been one of the international team of physicists developing the LISA gravitational wave detector, a project of the space agency ESA which is likely to have some NASA participation. He has carried out important research in an unusually wide range of fields: general relativity, astrophysics, the quantum theory of measurement, time travel, even the experimental details of the design of gravitational wave detectors. Panos Charitos (PC) and Spyros Argyropoulos (SA) met him in Geneva and discussed with him about the new window that gravitational waves open and the cosmological implications of this discovery.

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20 June 2017

The LISA trio of satellites to detect gravitational waves from space has been selected as the third large-class mission in ESA’s Science programme, while the Plato exoplanet hunter moves into development.

These important milestones were decided upon during a meeting of ESA’s Science Programme Committee today, and ensure the continuation of ESA’s Cosmic Vision plan through the next two decades.

The ‘gravitational universe’ was identified in 2013 as the theme for the third large-class mission, L3, searching for ripples in the fabric of spacetime created by celestial objects with very strong gravity, such as pairs of merging black holes.

Predicted a century ago by Albert Einstein's general theory of relativity, gravitational waves remained elusive until the first direct detection by the ground-based Laser Interferometer Gravitational-Wave Observatory in September 2015. That signal was triggered by the merging of two black holes some 1.3 billion light-years away. Since then, two more events have been detected.

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Image Credit: Virgo Collaboration

17 June 2017 -- For the first time, all three second generation interferometers---LIGO Hanford, LIGO Livingston, and Virgo---are simultaneously in a locked state. (When an interferometer is "locked" it means that an optical resonance is set up in the arm cavities and is producing a stable interference pattern at the photodetector.) Virgo is joining in an engineering mode, in preparation for the full triple-observing mode planned for later this summer. Congratulations, Virgo! - See more at:

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Results confirm new population of black holes

The Laser Interferometer Gravitational-wave Observatory (LIGO) has made a third detection of gravitational waves, ripples in space and time, demonstrating that a new window in astronomy has been firmly opened. As was the case with the first two detections, the waves were generated when two black holes collided to form a larger black hole.

GW170104 black hole size comparison
Schematic showing the relative 'sizes' (in Rs) of the black holes before and after merging.
The newfound black hole, formed by the merger, has a mass about 49 times that of our sun. This fills in a gap between the masses of the two merged black holes detected previously by LIGO, with solar masses of 62 (first detection) and 21 (second detection).

"We have further confirmation of the existence of stellar-mass black holes that are larger than 20 solar masses—these are objects we didn't know existed before LIGO detected them," says MIT's David Shoemaker, the newly elected spokesperson for the LIGO Scientific Collaboration (LSC), a body of more than 1,000 international scientists who perform LIGO research together with the European-based Virgo Collaboration. "It is remarkable that humans can put together a story, and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us. The entire LIGO and Virgo scientific collaborations worked to put all these pieces together."

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THREE OF A KIND Scientists have made a third detection of gravitational waves. A pair of black holes, shown above, fused into one, in a powerful collision about 3 billion light-years from Earth. That smashup churned up ripples in spacetime that were detected by the LIGO experiment.

Spacetime vibrations arrive from black hole collision 3 billion light-years away
BY EMILY CONOVER 11:00AM, JUNE 1, 2017

For a third time, scientists have detected the infinitesimal reverberations of spacetime: gravitational waves.

Two black holes stirred up the spacetime wiggles, orbiting one another and spiraling inward until they fused into one jumbo black hole with a mass about 49 times that of the sun. Ripples from that union, which took place about 3 billion light-years from Earth, zoomed across the cosmos at the speed of light, eventually reaching the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, which detected them on January 4.

“These are the most powerful astronomical events witnessed by human beings,” Michael Landry, head of LIGO’s Hanford, Wash., observatory, said during a news conference May 31 announcing the discovery. As the black holes merged, they converted about two suns’ worth of mass into energy, radiated as gravitational waves.

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A still image from a simulation that shows a black-hole binary inside a globular cluster. A new study examines how we can tell whether the black holes detected by LIGO were formed hierarchically from mergers of smaller black holes. [Northwestern Visualization/Carl Rodriguez]

By Susanna Kohler on 12 May 2017

The recent successes of the Laser Interferometer Gravitational-Wave Observatory (LIGO) has raised hopes that several long-standing questions in black-hole physics will soon be answerable. Besides revealing how the black-hole binary pairs are built, could detections with LIGO also reveal how the black holes themselves form?

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Extra dimensions hiding here

Signatures of extra dimensions that don’t normally affect the four dimensions we can observe could show up in the way they warp ripples in space-time

By Leah Crane

HIDDEN dimensions could cause ripples through reality by modifying gravitational waves – and spotting such signatures of extra dimensions could help solve some of the biggest mysteries of the universe.

Physicists have long wondered why gravity is so weak compared with the other fundamental forces. This may be because some of it is leaking away into extra dimensions beyond the three spatial dimensions we experience.

Some theories that seek to explain how gravity and quantum effects mesh together, including string theory, require extra dimensions, often with gravity propagating through them. Finding evidence of such exotic dimensions could therefore help to characterise gravity, or find a way to unite gravity and quantum mechanics – it could also hint at an explanation for why the universe’s expansion is accelerating.

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By Leah Crane

Put on the brakes. A spinning neutron star that shifts between two states slows at a faster rate in one of them – and gravitational waves may be responsible.

The neutron star J1023+0038 spins almost 600 times per second. But as its powerful magnetic field dissipates energy, it is slowing by about 76 rotations per second every billion years. This magnetic “spin-down” is normal, but sometimes J1023 slows at a faster rate.

The different rates are associated with two states the neutron star switches back and forth between: one where it emits mostly radio waves and one where it mainly gives off X-rays. No one knows why some neutron stars behave in this way. But when the star is emitting mostly X-rays, it slows down about 30 per cent faster.

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By Gabriel Popkin

APS April Meeting 2017 —

If the APS April Meeting 2016 was a champagne-soaked celebration for gravitational wave scientists, the 2017 meeting was more like spring training — there was lots of potential, but the real action is yet to come.

The Laser Interferometer Gravitational-Wave Observatory, or LIGO, launched the era of gravitational wave astronomy in February 2016 with the announcement of a collision between two black holes observed in September 2015. "I’m contractually obligated to show the slide [of the original detection] at any LIGO talk for at least another year," joked Jocelyn Read, a physicist at California State University, Fullerton, during her presentation at this year’s meeting.

The scientific collaboration that operates the two LIGO detectors netted a second merger between slightly smaller black holes on December 26, 2015. (A third "trigger" showed up in LIGO data on October 12, 2015, but ultimately did not meet the stringent "five-sigma" statistical significance standard that physicists generally insist on.)

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Kip Thorne (left) and Ronald Drever (middle), with Robbie Vogt, the first director of the LIGO project (1990)

Ronald Drever, one of the architects behind the first detection of gravitational waves, has died aged 85.

The Scottish physicist passed away peacefully in Edinburgh on Tuesday, following a short but rapid deterioration in his health.
Prof Drever is credited with doing some of the key early experimental work.

The sensing in 2015 of ripples in the fabric of space-time generated by merging black holes is seen as one of the major breakthroughs of our time.

His family announced the death with a short statement late on Wednesday: "We are extremely proud of Ronald and his scientific achievements; he was unique and unconventional but very caring with a strong sense of humour. He will be sadly missed by us all."

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Virgo stretches its 3-kilometer arms across the Tuscan plain near Pisa, Italy.
Virgo Collaboration/N. Baldocchi

By Daniel Clery

Feb. 16, 2017 , 2:00 PM

On 20 February, dignitaries will descend on Virgo, Europe’s premier gravitational wave detector near Pisa, Italy, for a dedication ceremony to celebrate a 5-year, €24 million upgrade. But the pomp will belie nagging problems that are likely to keep Virgo from joining its U.S. counterpart, the Laser Interferometer Gravitational-Wave Observatory (LIGO), in a hunt for gravitational wave sources that was meant to start next month. What has hobbled the 3-kilometer-long observatory: glass threads just 0.4 millimeters thick, which have proved unexpectedly fragile. The delay, which could last a year, is “very frustrating for everyone,” says LIGO team member Bruce Allen, director of the Max Planck Institute for Gravitational Physics in Hannover, Germany.

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LISA would use three spacecraft linked by lasers to detect passing gravitational waves. Credit: AEI/MM/exozet 

by Jeff Foust — February 7, 2017

WASHINGTON — A combination of scientific breakthroughs and technical accomplishments are making astronomers optimistic the European Space Agency will proceed with development of a space-based gravitational wave observatory.

A European consortium submitted to ESA in January a proposal for the development of the Laser Interferometer Space Antenna (LISA) mission for ESA’s third large mission, or L3, competition. LISA is widely considered the leading candidate to be selected for that mission for launch likely in the early 2030s.

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 LIGO Detection: Behind the scenes of the discovery of the decade

To celebrate the one-year anniversary of a discovery that changed the face of astronomy, on 7 February we feature the exclusive world premiere of a new documentary.

LIGO Detection reveals what unfolded behind the scenes between the detection of merging black holes on 14 September 2015, and five months later when LIGO announced it to the world

Click here to sign up to our newsletter and find out about exclusive content like this before anyone else.

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Following their discovery, the US White House Committee on Science, Space, and Technology asked LIGO Scientific Collaboration members to testify on the discovery, its meaning for science and society, and what the future may hold. From left to right: assistant director of the NSF's Directorate of Mathematical and Physical Sciences, Fleming Crim; LIGO lab director David Reitze; LIGO spokesperson Gabriela Gonzalez; and LIGO MIT director David Shoemaker. (Courtesy: LIGO Collaboration)

The Physics World 2016 Breakthrough of the Year goes to "the LIGO Scientific Collaboration for its revolutionary, first-ever direct observations of gravitational waves". Nine other achievements are highly commended and cover topics ranging from nuclear physics to material science and more.

Almost exactly 100 years after they were first postulated by Albert Einstein in his general theory of relativity, gravitational waves hit the headlines in 2016 as the US-based LIGO collaboration detected two separate gravitational-wave events using the Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO). The first observation was made on 14 September 2015 and was announced in February this year. A second set of gravitational waves rolled through LIGO's detectors on 26 December 2015, and this so-called "Boxing Day event" was announced in June this year. Gravitational waves are ripples in the fabric of space–time, and these observations mark the end of a decades-long hunt for these interstellar undulations.

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Nicolle R. Fuller/Science Photo Library

Black hole mergers captured by LIGO offer a chance to explore new physics.

Gravitational-wave data show tentative signs of firewalls or other exotic physics.

Zeeya Merali
09 December 2016

It was hailed as an elegant confirmation of Einstein’s general theory of relativity — but ironically the discovery of gravitational waves earlier this year could herald the first evidence that the theory breaks down at the edge of black holes. Physicists have analysed the publicly released data from the Laser Interferometer Gravitational-Wave Observatory (LIGO), and claim to have found “echoes” of the waves that seem to contradict general relativity’s predictions1.

The echoes could yet disappear with more data. If they persist, the finding would be extraordinary. Physicists have predicted that Einstein’s hugely successful theory could break down in extreme scenarios, such as at the centre of black holes. The echoes would indicate the even more dramatic possibility that relativity fails at the black hole’s edge, far from its core.

If the echoes go away, then general relativity will have withstood a test of its power — previously, it wasn’t clear that physicists would be able to test their non-standard predictions.

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by Shane L. Larson

The seas of the Cosmos are vast and deep. From our vantage point here on the shores of Earth, we have seen much that is beautiful, awe-inspiring, frightening, humbling, confusing, and enigmatic. The simple truth of astronomy is that it is a spectator sport. The only thing we can do, is watch the skies and wait for the next Big Thing to happen. We collect events, like bottle-caps or flowers, and add them to our collection. Each new addition is a mystery, a new piece of a puzzle that takes shape ever-so-slowly over time.

On 14 September 2015, the LIGO-Virgo collaboration announced that they had detected the first gravitational waves ever, and that those waves had been created by a pair of merging black holes far across the Cosmos.

Today, we have some more news: LIGO has detected the second gravitational wave event ever, and those waves were also created by a pair of merging black holes far across the Cosmos. But as is often the case with astronomy, we know what we’ve observed, but we still don’t know what it means.

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One hundred years ago, Albert Einstein predicted the existence of ripples in the fabric of space called gravitational waves. He didn't believe we could ever hear them; he thought they'd be too quiet.

But scientists have just proven Einstein wrong a second time.

More than 1,000 physicists recorded the first gravitational waves on September 14, 2015, yet spent months confirming the unprecedented signal, officially announcing their discovery on February 11, 2016.

On Wednesday, the international collaboration announced its second-ever detection of gravitational waves - and the alluring signs of a third.

The researchers behind the huge experiment that found these events, called the Laser Interferometer Gravitational-Wave Observatory (LIGO), think two black holes collided to create the cosmic reverberations heard trillions of miles away on Earth.

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 An artist’s conception of the LISA Pathfinder spacecraft in orbit at Lagrange Point 1. Photovoltaic solar cells on the top of the spacecraft provide power. Micronewton thrusters can be seen on the sides of the spacecraft. The test masses and laser interferometer readout system are located inside the spacecraft

David Reitze, LIGO Laboratory, California Institute of Technology, Pasadena, CA 91125, USA
June 7, 2016• Physics 9, 63

The first results from the LISA Pathfinder mission demonstrate that two test masses can be put in free fall with a relative acceleration sufficiently free of noise to meet the requirements needed for space-based gravitational-wave detection.

The announcement in February 2016 that the Laser Interferometer Gravitational-wave Observatory (LIGO) had detected gravitational waves from the merger of two black holes stunned and electrified much of the physics and astronomy communities [1]. However, while all eyes were turned toward LIGO, the LISA Pathfinder (LPF)—a technology demonstration mission for the Laser Interferometer Space Antenna (LISA) gravitational-wave detector [2]—was quietly but convincingly paving the way toward the next revolution in gravitational-wave astronomy more than 1.5 million kilometers away from Earth. After a six-month program that began with the launch of the spacecraft in early December 2015, the team behind LPF has now announced the first results from the mission [3]. Following a 50-day journey to Lagrange Point 1 of the Sun-Earth system, LPF settled into orbit to begin a series of spacecraft acceptance tests and an observing campaign to measure the limits with which two test masses can achieve free fall.

LPF was designed to test many of the key technologies needed by LISA. LISA will target a much lower gravitational-wave frequency band than LIGO, from about 100 mHz to 1 Hz. This regime is sensitive to gravitational waves from mergers of intermediate to massive black holes in the range of 10^4 to 10^7 solar masses, as well as from mergers of black holes that have an extreme mass ratio (in which one black hole is much more massive than the other). But it necessitates a space-based platform to avoid low-frequency noise sources arising on Earth, which easily overwhelm the signal from such waves. These mergers will provide the most stringent tests of General Relativity in the strong-gravity regime.

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By collecting gravitational wave data at facilities such as LIGO in the US, researchers can better understand the constantly changing nature of the universe. Image credit: LIGO Caltech

The sooner-than-expected discovery of gravitational waves, announced in February, has given a new impetus to scientists in the field, who are now working to make sense of what it means not only for their research but also for our understanding of Einstein’s theory of general relativity.

Imagine two figure skaters on the ice, spiralling in closer and closer toward one another, until they finally form one spinning clump. But you can’t see them. Your only clue to their motion is by listening to how the ice subtly cracks and contorts under their movement over the roar of a packed crowd.

That’s the sort of challenge scientists are up against when they look for gravitational waves – ripples in the fabric of space which are given off during the merger of pairs of black holes or neutron stars, predicted by Einstein’s theory of general relativity.

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By Gabriel Popkin

APS April Meeting 2016 — Members of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration took a victory lap of sorts at the APS April Meeting 2016 in Salt Lake City, Utah. Talk after talk began with slides showing the now-famous signal from GW150914, the formal name for the September 14, 2015 detection of gravitational waves from two black holes that merged 1.3 billion years ago.

“For the first time when I present this talk, I can start with a discovery, not just upper limits,” said Alessandra Corsi, an astrophysicist at Texas Tech University.

But speakers quickly pivoted to new astrophysics emerging from GW150914 and LVT151012, a second candidate event that appeared in LIGO data but did not reach the critical “5-sigma” statistical threshold needed to claim a true detection. Researchers also shared new ideas for peering deeper into the universe and increasing the frequency spectrum that gravitational-wave detectors can probe.

For astrophysics, GW150914 heralded a series of firsts — not just the first detection of a gravitational wave, but also the the first proof that black holes form merging pairs (only inspiraling neutron stars had been previously seen), and the first evidence of black holes more than 25 times the mass of the sun. The large sizes of the merging black holes also revealed that their source stars were low in heavy elements, and that their spins were substantially lower than the maximum possible value allowed under general relativity.

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The nonprofit Simons Foundation will fund a new observatory to search for signs of stretching in the very early universe
By Clara Moskowitz on May 12, 2016

How did it all begin? The origin of the cosmos is probably the biggest mystery in science—but amazingly, researchers do have some hard evidence to consult in their attempts to solve it. The cosmic microwave background (CMB), a microwave fog that pervades space, is the oldest light in existence—it was released about 13.7 billion years ago when the extremely hot and dense baby universe cooled enough to allow photons to travel freely for the first time. That was about 380,000 years after the big bang, and the light has been flying through space ever since. Although the light itself is already unimaginably ancient, it may preserve a record of things that happened even earlier—specifically, it might contain imprints from gravitational waves that may have ripped through the cosmos in the very first moments of space and time.

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Space-based detector draws interest, but regulatory hurdles might complicate a partnership.

Elizabeth Gibney
04 May 2016

In the wake of the historic detection of gravitational waves by a terrestrial US experiment, a space-borne European effort is drawing interest from a range of parties. But although advisers to the European Space Agency (ESA) recommended increasing international contributions to the billion-euro gravitational-wave detector on 12 April, regulatory hurdles may hinder proposed partnerships with the United States and China.

In February, researchers working on the US-based Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had detected ripples in space-time that had been produced by the merger of two black holes. The space-based observatory planned by ESA would be able to detect ripples with much lower frequencies than would be possible on Earth, bringing into view a greater variety of astronomical events, including mergers between supermassive black holes.

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BY KARAN JANI ON 07/05/2016

Kip Stephen Thorne is a noted astrophysicist and a central figure in the legacy of gravitational physics research. He is the Richard P. Feynman Professor of Theoretical Physics, Emeritus, at the California Institute of Technology. He has made seminal contributions to theories underpinning the origin, characteristics and properties of blackholes, and theorised about the existence and behaviour of wormholes. Thorne is also famously interested in communicating ideas in advanced physics to the general public. He has written many popular books, notably Black Holes and Time Warps (1994), and helped helped Carl Sagan ideate on wormhole travel for the latter’s novel Contact (1985). The science behind the 2014 film Interstellar was defined by Thorne.

Even more recently, he has been in the limelight for the LIGO experiment’s discovery of gravitational waves. Thorne was instrumental in developing the idea of the instrument (alongside Rai Weiss and Ronald Drever), securing its funding, evolving a thrumming community of researchers around it, and getting it going. Karan Jani, a doctoral researcher at the Centre for Relativistic Astrophysics, Georgia Institute of Technology, and a member of the team that discovered the gravitational waves, spoke to Thorne on behalf of The Wire (from the lab of Laura Cadonati, Chair of the LIGO Data Analysis Council). The full interview (edited for clarity) follows.

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A European Space Agency effort to try to detect gravitational waves in space is not only technically feasible but compelling, a new report finds.

A panel of experts was asked to perform a "sanity check" on the endeavour, which is likely to cost well in excess of one billion euros.
The Gravitational Observatory Advisory Team says it sees no showstoppers.

It even suggests ESA try to accelerate the project from its current proposed launch date in 2034 to 2029.

Whether that is possible is largely a question of funding. Space missions launch on a schedule that is determined by a programme's budget.

"But after submitting our report, Esa came back to us and asked what we thought might be technically possible, putting aside the money," explained Goat chairman, Dr Michael Perryman.

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IN BRIEF

Scientists at Advanced LIGO believe they may be able to begin discerning as many as 2,000 faint echoes of black hole mergers within three years.

SEARCHING FOR MEANING IN A SEA OF NOISE

The long-awaited detection of gravitational waves was announced with a clear and unmistakable note—it was a “chirp” that noticeably rose above the welter of background noise. It was the swan song of two roughly 30-Solar-mass black holes coalescing into a single spacetime-warping monster some 1.3 billion light-years away.

But such chirps may be few and far between, and now scientists at the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) think they may be able to discern the distant roar of multiple black hole mergers in that background noise.

The study, detailed in the April 1 issue of Physical Review Letters, predicts that scientists may be able to discover these ephemeral signals in as little as three years.

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(Phys.org)—The research team working with the LIGO project has proposed that the data gleaned from the discovery of gravity waves last year allows for calculating the likely level of cosmic background noise due to gravitational waves, and that it is much greater than previous models have suggested. In their paper published in Physical Review Letters, researchers with the LIGO Scientific Collaboration along with a companion group from the Virgo Collaboration, describe their reasoning behind their estimates and why they believe they will be able to offer more support for their theory within just a few years.

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Scientists are sitting on top of the world after this monumental discovery and are eager to keep exploring the universe

More than a billion years ago, in a galaxy far, far away, two black holes executed the final steps in a fast-footed pas de deux, concluding with a final embrace so violent it released more energy than the combined output of every star in every galaxy in the observable universe. Yet, unlike starlight, the energy was dark, being carried by the invisible force of gravity. On September 14, 2015, at 5:51 a.m. Eastern Daylight Time, a fragment of that energy, in the form of a “gravitational wave,” reached Earth, reduced by its vast transit across space and time to a mere whisper of its thunderous beginning

As far as we know, Earth has been bathed in this type of gravitational disturbance before. Frequently. The difference this time is that two stupendously precise detectors, one in Livingston, Louisiana, and the other in Hanford, Washington, were standing at the ready. When the gravitational wave rolled by, it tickled the detectors, providing the unmistakable signature of colliding black holes on the other side of the universe and marking the beginning of a new chapter in humankind’s exploration of the cosmos.

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Though the recent discovery of GW150914 is a thrilling success in the field of gravitational-wave astronomy, LIGO is only one tool the scientific community is using to hunt for these elusive signals. After 10 years of unsuccessful searching, how likely is it that pulsar-timing-array projects will make their own first detection soon?

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Successful test drive for space-based gravitational-wave detector
Mission paves the way for planned €1-billion space observatory.

Elizabeth Gibney
25 February 2016

Scientists have long dreamed of launching a constellation of detectors into space to observe gravitational waves — the ripples in space-time predicted by Albert Einstein and observed for the first time earlier this month.

That dream is now a step closer to reality. Researchers working on a €400-million (US$440-million) mission to try out the necessary technology in space for the first time — involving firing lasers between metal cubes in free fall — have told Nature that the initial test drive is performing just as well as they had hoped.

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LISA Pathfinder operating in space

24 February 2016

On Monday, the two cubes housed in the core of ESA’s LISA Pathfinder were left to move under the effect of gravity alone – another milestone towards demonstrating technologies to observe gravitational waves from space.

It has been an intense couple of months for LISA Pathfinder. After launch on 3 December and six burns to raise the orbit, it finally reached its work site – 1.5 million km from Earth towards the Sun – in January, and the team of engineers and scientists started to switch on and test its systems.

One of the most delicate operations entailed releasing the two test masses from the mechanisms that kept them in place during ground handling, launch and cruise.

See full texthttp://www.esa.int/Our_Activities/Space_Science/Freefall_achieved_on_LISA_Pathfinder

Mission paves the way for planned €1-billion space observatory.

Elizabeth Gibney
25 February 2016

Scientists have long dreamed of launching a constellation of detectors into space to detect gravitational waves – ripples in space-time first predicted by Albert Einstein and observed for the first time earlier this month.

That dream is now a step closer to reality. Researchers working on a €400 million (US$440 million) mission to try out the necessary technology in space for the first time – involving firing lasers between metal cubes in freefall – have told Nature that the initial test-drive is performing just as well as they had hoped.

“I think we can now say that the principle has worked,” says Paul McNamara, project scientist for the LISA Pathfinder mission, which launched in December. “We believe that we now are in a good shape to look to the future and look to the next generation.”

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A simulated view of gravitational waves rippling out from merging black holes. The reddish waves correspond to those recently detected from a real black-hole merger by the Laser Interferometer Gravitational-wave Observatory (LIGO).
Credit: NASA/C. Henze

The Future of Gravitational Wave Astronomy
Fully opening this new window on the universe will take decades—even centuries
By Lee Billings on February 12, 2016

A century ago, when Albert Einstein first predicted the existence of gravitational waves—subtle ripples in spacetime produced by massive objects hurtling through the cosmos—he also guessed they could not ever be seen. Though the echoes of distant celestial symphonies must ripple through the very fabric of reality, Einstein thought their ethereal harmonies were destined to remain eternally unheard.

On Thursday, scientists using the Laser Interferometer Gravitational-wave Observatory (LIGO) proved Einstein both right and wrong, announcing their detection of the first note in a cosmic symphony he predicted no one would ever hear. It was a burbling chirp of gravitational waves produced by the cataclysmic birth of a black hole from the merger of two smaller ones. Emitted in a distant galaxy when multicellular life was just beginning to populate the Earth, the waves traveled at the speed of light for more than a billion years to at last wash over our planet last September, taking just seven milliseconds to traverse the distance between LIGO’s twin listening stations in Louisiana and Washington State.

Now, unlike Einstein a century ago who could scarcely imagine gravitational waves ever being seen, the scientists hunting the elusive spacetime ripples already have big plans for more detectors and observatories in the near and far future.
“Imagine light having never been collected in a photograph,” says Janna Levin, an astrophysicist at Barnard College of Columbia University and author of a forthcoming book about LIGO. “The first thing people want to do is just to capture the recording, which is what LIGO has done.”

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The LIGO facility in Livingston, Louisiana, has a twin in Hanford, Washington   © ATMOSPHERE AERIAL

By Adrian ChoFeb. 5, 2016 , 2:30 PM

It's just a rumor, but if specificity is any measure of credibility, it might just be right. For weeks, gossip has spread around the Internet that researchers with the Laser Interferometer Gravitational-Wave Observatory (LIGO) have spotted gravitational waves—ripples in space itself set off by violent astrophysical events. In particular, rumor has it that LIGO physicists have seen two black holes spiraling into each other and merging. But now, an email message that ended up on Twitter adds some specific numbers to those rumors. The author says he got the details from people who have seen the manuscript of the LIGO paper that will describe the discovery.

"This is just from talking to people who said they've seen the paper, but I've not seen the paper itself," says Clifford Burgess, a theoretical physicist at McMaster University in Hamilton, Canada, and the Perimeter Institute for Theoretical Physics in nearby Waterloo. "I've been around a long time, so I've seen rumors come and go. This one seems more credible."

According to Burgess's email, which found its way onto Twitter as an image attached to a tweet from one of his colleagues, LIGO researchers have seen two black holes, of 29 and 36 solar masses, swirling together and merging. The statistical significance of the signal is supposedly very high, exceeding the "five-sigma" standard that physicists use to distinguish evidence strong enough to claim discovery. LIGO consists of two gargantuan optical instruments called interferometers, with which physicists look for the nearly infinitesimal stretching of space caused by a passing gravitational wave. According to Burgess's email, both detectors spotted the black hole merger with the right time delay between them.

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The 4km "west" arm of the LIGO interferometer stretches into the foggy distance.

Ars goes inside ground zero of the search for gravitational waves.

by Eric Berger - Feb 4, 2016 2:00pm CET

LIVINGSTON, La.—The rain began to fall as Joe Giaime and I scrambled down a lonely rise, back toward the observatory’s main building. It wasn’t so much rain as a hard mist, characteristic of the muggy weather southern Louisiana often sees in January when moisture rolls inland from the Gulf of Mexico. As gray clouds fell like a shroud over the loblolly pines all around us, Giaime mused, “Well, I guess you’ve already gathered that we’re in the middle of nowhere."

Middle of nowhere happens to be ground zero in the search for gravitational waves, which were first posited by Albert Einstein a century ago and may soon become one of the hottest fields in science. Livingston is remote in terms of geography, but as humans scan the heavens for gravitational waves this forest is practically the center of the physics universe.

Because of general relativity, we understand that large masses curve spacetime, kind of like standing in the middle of a trampoline distorts the fabric. When massive, dense objects in space accelerate, such as black holes or neutron stars, they create ripples in the fabric of spacetime. These ripples carry gravitational radiation away from the very massive objects, and the radiation then propagates through the Universe. This Louisiana observatory, the Laser Interferometer Gravitational-Wave Observatory or LIGO, exists to try to measure these subtle ripples.

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by Shane L. Larson

Each morning, I roll out of bed, dutifully feed the three cats that own me, help my fourth-grader get her backpack put together for the day and put my daily secret note in her lunch, enjoy a few brief moments over morning coffee with my spouse, and then it is off to work.

For my day job, I’m a scientist. My friends and I work in a completely new branch of astronomy called gravitational wave astronomy. Our express goal is to detect a phenomenon that was predicted almost a century ago by Einstein: the undulations and propagating ripples in the fabric of spacetime that signify the dynamic motion of matter in the Cosmos.

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Rumor of gravitational wave discovery is just that, source says

By Adrian Cho  Jan. 12, 2016

Science Magazine

If you follow physics, you have likely heard the rumor by now: Physicists working with a pair of gigantic detectors have finally discovered gravitational waves—ripples in space and time set off when, say, two massive neutrons stars spiral into each other—and have only to announce it. It would be a sure-fire Nobel Prize–winning discovery and the rumor sounds plausible. Sensing those waves is exactly what a $500 million project called the Laser Interferometer Gravitational-Wave Observatory (LIGO) was built to do. Numerous news outlets have reported the rumor, prompted by Twitter posts by Lawrence Krauss, a theoretical physicist and author at Arizona State University, Tempe.

There's a qualification, however: By his own account, Krauss has spoken to nobody in the 900-member LIGO Scientific Collaboration.

"I never said I've talked to anybody in the collaboration," he tells ScienceInsider. "That's why I used the word rumor. I don't know how to be clearer."

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IF TRUE, THE DISCOVERY WOULD SUPPORT ONE OF EINSTEIN'S MAJOR PREDICTIONS.
By Sarah Fecht Posted Yesterday at 11:10pm

In September, the Caltech theoretical physicist Lawrence Krauss tweeted:

@LKrauss1 amazing if true, but as scientists shouldn't we avoid spreading rumors, especially in a public space, and wait to know the facts?
1:31 PM - 26 Sep 2015

The folks on the LIGO experiment neither confirmed nor denied the rumor, and in Krauss's rumor-mongering raised hackles in the astrophysics community.

But now he's back at it again:

My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.
4:46 PM - 11 Jan 2016

There's plenty of reason to remain skeptical--we won't know for sure whether the rumor is true until we hear from the researchers on the experiment. If it does turn out to be true, it would be a very exciting finding.

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03 December 2015

ESA's LISA Pathfinder lifted off earlier today on a Vega rocket from Europe's spaceport in Kourou, French Guiana, on its way to demonstrate technology for observing gravitational waves from space.

Gravitational waves are ripples in the fabric of spacetime, predicted a century ago by Albert Einstein's General Theory of Relativity, published on 2 December 1915.
Einstein's theory predicts that these fluctuations should be universal, generated by accelerating massive objects. However, they have not been directly detected to date because they are so tiny. For example, the ripples emitted by a pair of orbiting black holes would stretch a million kilometre-long ruler by less than the size of an atom.

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08 October 2015
LISA Pathfinder, ESA's demonstrator for space-based observations of gravitational waves, has arrived at Europe's spaceport in Kourou, French Guiana, ahead of a launch currently foreseen for 2 December.

Once operating in space, LISA Pathfinder will pave the way for future missions by testing critical concepts and technologies related to the detection of gravitational waves, ripples in spacetime, the very fabric of the Universe. To do so, it will put two small gold-platinum cubes in a near-perfect gravitational free-fall through space, and control and measure their motions with unprecedented accuracy.
LISA Pathfinder consists of a science module, containing the core elements of the science experiment, that will be transferred by a separable propulsion module to its operational Lissajous orbit around the Lagrange point L1, 1.5 million kilometres away from Earth in the direction of the Sun.

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An improbable rumour has started that the observatory has already made a discovery — but even if true, the signal could be a drill.

Davide Castelvecchi
30 September 2015

On 25 September, a sensational rumour appeared on Twitter: Lawrence Krauss, a cosmologist, reported hearing that the world’s largest gravitational-wave observatory had seen a signal, barely a week after its official re-opening.

The rumour had been spreading around physics circles for at least a week. If it is true, and if the signal seen by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) genuinely represents the signature of a gravitational wave, it would confirm one of the most-elusive and spectacular predictions of the general theory of relativity almost exactly 100 years after Albert Einstein first proposed it.

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Advanced Ligo represents one of the most sensitive measuring systems ever devised

The experiment that should finally detect ripples in the fabric of space-time is up and running.
Labs in the US states of Washington and Louisiana began "listening" on Friday for the gravitational waves that are predicted to flow through the Earth when violent events occur in space.
The Advanced Ligo facilities have just completed a major upgrade.
Scientists believe this will now give them the sensitivity needed to pick up what should be a very subtle signal.
The theoretical physicist Kip Thorne, one of the pioneers behind the experiment, went so far as to say that it would be "quite surprising" if the labs made no detection.
"We are there; we are in the ball park now. It's clear that this is going to be pulled off," he confidently told The Documentary programme on the BBC World Service.

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The Advanced LIGO begins operations this week, after 7 years of enhancement.
The Advanced LIGO Project, a major upgrade of the Laser Interferometer Gravitational-Wave Observatory, is completing its final preparations before the initiation of scientific observations, scheduled to begin in mid-September. Designed to observe gravitational waves—ripples in the fabric of space and time—LIGO, which was designed and is operated by Caltech and MIT with funding from the National Science Foundation (NSF), consists of identical detectors in Livingston, Louisiana, and Hanford, Washington.

- See more at: http://www.caltech.edu/news/advanced-ligo-begin-operations-47898#sthash.a7JhFOit.dpuf

An illustration of two black holes orbiting one another. The black hole in the center of the image is starved of gas by the black hole at the left, making the gas cloud of the black hole on the left brighter.ILLUSTRATION BY ZOLTAN HAIMAN, ADAPTED FROM FARRIS ET AL. 2014

By DENNIS OVERBYE
SEPTEMBER 16, 2015
The apocalypse is still on, apparently — at least in a galaxy about 3.5 billion light-years from here.

Last winter a team of Caltech astronomers reported that a pair of supermassive black holes appeared to be spiraling together toward a cataclysmic collision that could bring down the curtains in that galaxy.

The evidence was a rhythmic flickering from the galaxy’s nucleus, a quasar known as PG 1302-102, which Matthew Graham and his colleagues interpreted as the fatal mating dance of a pair of black holes with a total mass of more than a billion suns. Their merger, the astronomers calculated, could release as much energy as 100 million supernova explosions, mostly in the form of violent ripples in space-time known as gravitational waves that would blow the stars out of that hapless galaxy like leaves off a roof.

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LIGO experiment now has better chance of detecting ripples in space-time.

Davide Castelvecchi

Almost 100 years after Einstein presented the general theory of relativity in a Berlin lecture theatre, the quest to spot the gravitational waves he predicted may be entering its final stages.

This week, the world’s largest gravitational-wave facility is expected to start collecting data again after a 5-year US$200-million overhaul. The Laser Interferometer Gravitational-Wave Observatory (LIGO) searched fruitlessly for these cosmic ripples for almost a decade in the 2000s. But the odds that its improved version — known as Advanced LIGO — will detect any waves in the next three months may be as high as one in three, according to some of the physicists involved in the experiments.

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ABOUT THIS IMAGE:
This artistic illustration is of a binary black hole found in the center of the nearest quasar host galaxy to Earth, Markarian 231. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars. Quasars have the most luminous cores of active galaxies and are often fueled by galaxy collisions.

Hubble observations of the ultraviolet light emitted from the nucleus of the galaxy were used to deduce the geometry of the disk, and astronomers were surprised to see light diminishing close to the central black hole. They deduced that a smaller companion black hole has cleared out a donut hole in the accretion disk, and the smaller black hole has its own mini-disk with an ultraviolet glow.

Astronomers using NASA's Hubble Space Telescope have found that Markarian 231 (Mrk 231), the nearest galaxy to Earth that hosts a quasar, is powered by two central black holes furiously whirling about each other.

The finding suggests that quasars — the brilliant cores of active galaxies — may commonly host two central supermassive black holes that fall into orbit about one another as a result of the merger between two galaxies. Like a pair of whirling skaters, the black-hole duo generates tremendous amounts of energy that makes the core of the host galaxy outshine the glow of the galaxy's population of billions of stars, which scientists then identify as quasars.

Scientists looked at Hubble archival observations of ultraviolet radiation emitted from the center of Mrk 231 to discover what they describe as "extreme and surprising properties."

If only one black hole were present in the center of the quasar, the whole accretion disk made of surrounding hot gas would glow in ultraviolet rays. Instead, the ultraviolet glow of the dusty disk abruptly drops off towards the center. This provides observational evidence that the disk has a big donut hole encircling the central black hole. The best explanation for the observational data, based on dynamical models, is that the center of the disk is carved out by the action of two black holes orbiting each other. The second, smaller black hole orbits in the inner edge of the accretion disk, and has its own mini-disk with an ultraviolet glow.

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In 2000, Betsy Weaver got hooked on a vision of things unseen.

As a student at Washington State University, Weaver’s physics program was visited by a group of scientists who lectured on the search into deep, deep, deep outer space. They spoke of phenomena mapped out by Albert Einstein, but so far undetected by humankind. Among these concepts, one stood out: Gravity waves.

Einstein’s math says they exist. Today’s astrophysicists agree. Gravity waves are transmitted from black holes and colliding neutron stars, neither of which has ever “seen” for real. Their existence could open the door to a new way of studying space, beyond optical and radio astronomy, because they can punch through astronomical obstacles that block light, noise and electro-magnetic waves.

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The LISA Pathfinder spacecraft is due to set off in autumn 2015 in a bid to prove that it is possible to observe gravitational waves in space. This is the latest step in an incredible journey to spot these ripples in spacetime that were first predicted by Albert Einstein 100 years ago.

If we can manage to capture these waves, then we should be able to observe some of the most violent events in the cosmos, such as black holes colliding and galaxies merging.

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Scientists hope a $200m upgrade to LIGO will bring them nearer to directly observing gravitational waves. (Courtesy: LIGO/Caltech)

A $200m upgrade to the Laser Interferometer Gravitational-wave Observatory (LIGO) has been completed, with the facility set for observations in the coming months as it aims to be the first to detect a gravitational wave. Dubbed Advanced LIGO, it consists of two separate telescopes in the US – the Livingston observatory in Louisiana and the Hanford observatory in Washington state – that use laser interferometers to search for gravitational waves.
According to Einstein's general theory of relativity, gravitational waves are effectively ripples in space–time that travel as a wave. While none have ever been directly detected, scientists have observed a loss of energy as two neutron stars – the dense cores of once-massive stars – spiral toward each other. That energy loss is precisely what Einstein's equations predict would be emitted as gravitational radiation.

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 An aerial view shows the LIGO Hanford facility near Richland, Washington.

After seven years of upgrades, the Advanced Laser Interferometer Gravitational Wave Observatories were dedicated on Tuesday at the LIGO Hanford facility near Richland, Washington.

The facilities are located amid the tumbleweeds of southeastern Washington and the pines of southeastern Louisiana. They're designed to detect the faint signature of gravitational waves given off by supernovas, black hole collisions and other cosmic crashes.

Albert Einstein's general theory of relativity predicts that such waves should exist, but they have never been detected directly. The Advanced LIGO experiment, funded by the National Science Foundation and operated by Caltech and MIT, is expected to change that. It could do for gravitational waves what Europe's Large Hadron Collider did for the equally elusive Higgs boson.

....

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photo credit: An artist's conception of a black hole binary in a heart of a quasar, with the data showing the periodic variability superposed / Santiago Lombeyda/Caltech Center for Data-Driven Discovery

An unusual, repeating light signal in the distance may be coming from the final stages of a merger between two supermassive black holes. At just a few hundredths of a light-year apart, they could be merging in a mere one million years. An event like this has been predicted based on theory, but has never been observed before, according to a new study published in Nature this week.

The supermassive black holes at the center of most large galaxies (including ours) appear to co-evolve with their host galaxies: As galaxies merge, their black holes grow more massive too. Since we can’t actually see black holes, researchers look for their surrounding bands of material called accretion disks, which are produced by the intense pull of the black hole’s gravity. The disks of supermassive black holes can release vast amounts of heat, X-rays, and gamma rays that result in a quasar—one of the most luminous objects in the universe.

Caltech’s Matthew Graham and colleagues noticed the light signal coming from quasar PG 1302-102 while studying variability in quasar brightness using data from the Catalina Real-Time Transient Survey, which continuously monitored 500 million celestial light sources across 80 percent of the sky with three ground telescopes.

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Ancient ripples in the fabric of the space square off against soot in the galaxy

NOT-SO-CLEAR SKIES The signal that BICEP2 researchers interpreted as gravitational waves may be due to interstellar dust. The Planck satellite mapped dust in the entire sky. The map shows the sky above the plane of the Milky Way (left) and below the galaxy’s plane (right). Planck found areas heavily contaminated by dust (red) and regions that are relatively clean (blue). The black box shows where BICEP2 searched for gravitational waves.

Gravitational waves from the Big Bang captured worldwide attention in 2014. But then interstellar dust clouds stole
the show.

Detection of such waves — ripples in the fabric of space — would be direct evidence for the theory of cosmological inflation, a brief epoch immediately after the Big Bang when the visible universe abruptly swelled to at least 1075 times its initial volume.

In March, astrophysicists thought they had captured their elusive gravitational wave quarry. Researchers with the BICEP2 project reported swirling patterns in the alignment of electromagnetic waves in the cosmic microwave background, or CMB, the primordial light released into the universe about 380,000 years after the Big Bang (SN: 4/5/14, p. 6). Those patterns supposedly reflected the influence of gravitational waves launched during the epoch of inflation. 

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The sun sets behind BICEP2, in the foreground, and the South Pole Telescope, in the background. (Steffen Richter/VagabondPix.com)

A new analysis has dynamited a much-hyped discovery of “gravitational waves” from the dawn of time. What had seemed to be a major breakthrough in cosmology, one that incited loose talk of Nobel prizes, now appears to have been a case of scientists over-interpreting their data.

Last March, in a highly anticipated news conference at Harvard, scientists with an experiment called BICEP2 revealed that their South Pole telescope had scanned the background radiation of the universe and made a dazzling discovery: The ancient light had apparently been polarized by gravitational waves emitted in the initial moment after the Big Bang, when the tiny, dense universe expanded violently.

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 A simulation of gravitational waves produced by two orbiting black holes. Photograph: Ligo Collaboration

Here’s a date for your diary: 1 January 2017. It’s the day that physicists are predicting for a great scientific breakthrough: the first direct detection of gravitational waves.

Even if you have not yet heard about gravitational waves, you are going to in the coming years. When they are detected, it will revolutionise our investigation of the universe.

It will be the equivalent of astronomers discovering a new sense. With telescopes, they can already see the universe. By detecting gravitational waves, they will be able to ‘listen’ to it as well. We would be able to ‘hear’ stars colliding with one another, the destruction of matter falling into black holes and the catastrophic detonation of distant massive stars.

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The twin 4-kilometer arms of LIGO Livingston embrace a working forest, where logging generates vibrations that the instrument must damp out.

After decades of effort, physicists say they are on the verge of detecting ripples in spacetime called gravitational waves, whose existence Albert Einstein himself predicted nearly a century ago. Researchers working on the Laser Interferometer Gravitational-Wave Observatory (LIGO) will use enormous instruments in Livingston, Louisiana, and Hanford, Washington, to look for the gravitational waves set off when two neutron stars spiral into each other. LIGO ran from 2002 to 2010 and saw nothing, but those Initial LIGO instruments aimed only to prove that the experiment was technologically feasible, physicists say. Now, they're finishing a $205 million rebuild of the detectors, known as Advanced LIGO, which should make them 10 times more sensitive and, they say, virtually ensure a detection. Such an observation would open up a whole new type of astronomy—and likely bag a Nobel Prize.

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