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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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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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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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.

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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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