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.

See full text

The black hole, as illustrated in the movie Interstellar, shows an event horizon fairly accurately for a very specific class of rotating black holes. Image credit: Interstellar / R. Hurt / Caltech.

The Event Horizon Telescope has come online and taken its data. Now, we wait for the results.

Black holes are some of the most incredible objects in the Universe. There are places where so much mass has gathered in such a tiny volume that the individual matter particles cannot remain as they normally are, and instead collapse down to a singularity. Surrounding this singularity is a sphere-like region known as the event horizon, from inside which nothing can escape, even if it moves at the Universe’s maximum speed: the speed of light. While we know three separate ways to form black holes, and have discovered evidence for thousands of them, we’ve never imaged one directly. Despite all that we’ve discovered, we’ve never seen a black hole’s event horizon, or even confirmed that they truly had one. Next year, that’s all about to change, as the first results from the Event Horizon Telescope will be revealed, answering one of the longest-standing questions in astrophysics.

See full text

Natalie Wolchover -- December 18, 2017

The mother of all string theories passes a litmus test that, so far, no other candidate theory of quantum gravity has been able to match.

It’s not easy being a “theory of everything.” A TOE has the very tough job of fitting gravity into the quantum laws of nature in such a way that, on large scales, gravity looks like curves in the fabric of space-time, as Albert Einstein described in his general theory of relativity. Somehow, space-time curvature emerges as the collective effect of quantized units of gravitational energy — particles known as gravitons. But naive attempts to calculate how gravitons interact result in nonsensical infinities, indicating the need for a deeper understanding of gravity.

String theory (or, more technically, M-theory) is often described as the leading candidate for the theory of everything in our universe. But there’s no empirical evidence for it, or for any alternative ideas about how gravity might unify with the rest of the fundamental forces. Why, then, is string/M-theory given the edge over the others?

See full text

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.

See full text

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].

See full text

Credits: ESO

IN BRIEF

• Vacuum birefringence has been observed by a team of scientists for the first time ever using the European Southern Observatory's (ESO) Very Large Telescope (VLT).
• The team observed neutron star RX J1856.5-375, which is about 400 light-years from Earth, with just visible light, pushing the limits of existing telescope technology.

A LITTLE LESS STRANGE

Vacuum birefringence is a weird quantum phenomenon that has only ever been observed on an atomic scale. It occurs when a neutron star is surrounded by a magnetic field so intense, it’s given rise to a region in empty space where matter randomly appears and vanishes.

This polarization of light in a vacuum due to strong magnetic fields was first thought to be possible in the 1930s by physicists Werner Heisenberg and Hans Heinrich Euler as a product of the theory of quantum electrodynamics (QED). The theory describes how light and matter interact.

Now, for the first time ever, this strange quantum effect has been observed by a team of scientists from INAF Milan (Italy) and from the University of Zielona Gora (Poland).

Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT), a research team led by Roberto Mignani observed neutron star RX J1856.5-375, which is about 400 light-years from Earth.

See full text

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.

See full text

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.

See full text

FREE-FALLIN’ Scientists compared the acceleration of two objects in free fall in a satellite orbiting 710 kilometers above Earth (illustrated)

Equivalence principle holds up inside an orbiting satellite
BY EMILY CONOVER 6:00AM, DECEMBER 4, 2017

Galileo’s most famous experiment has taken a trip to outer space. The result? Einstein was right yet again. The experiment confirms a tenet of Einstein’s theory of gravity with greater precision than ever before.

According to science lore, Galileo dropped two balls from the Leaning Tower of Pisa to show that they fell at the same rate no matter their composition. Although it seems unlikely that Galileo actually carried out this experiment, scientists have performed a similar, but much more sensitive experiment in a satellite orbiting Earth. Two hollow cylinders within the satellite fell at the same rate over 120 orbits, or about eight days’ worth of free-fall time, researchers with the MICROSCOPE experiment report December 4 in Physical Review Letters. The cylinders’ accelerations match within two-trillionths of a percent.

See full text

RUSSELL MCLENDON -- November 20, 2017

From explaining the mysteries of nature to proving the power of daydreams, Albert Einstein gave the world a lot to be grateful for.

On Thanksgiving Day in 1915, a 36-year-old physicist named Albert Einstein submitted a paper to the Proceedings of the Prussian Academy of Sciences in Berlin. That paper — titled "Die Feldgleichungen der Gravitation," or "The Field Equations of Gravity" — was a scientific blockbuster, unveiling equations that govern the universe.

Einstein was in Germany at the time, so the U.S. holiday of Thanksgiving may not have been top of mind. (Also, he was probably a bit distracted by revolutionizing modern physics and astronomy.) Yet even if Einstein wasn't thinking of Thanksgiving on that fateful November day, it was one of many moments in his life that would inspire gratitude from people around the world, even a century later.

Physicists and astronomers are understandably thankful for Einstein's work, as are many other scientists whose careers hinge on his game-changing equations. But Einstein isn't just an esoteric hero for scholars — he's one of the most famous scientists of all time, serving as a global icon and synonym for ingenuity itself.

Hyperbole is common when describing the impact of historical figures, yet in Einstein's case, the superlatives are generally apt. He really was a rare genius who transformed our understanding of space, time and gravity, and his discoveries really did enable a wide array of modern technology. He also left a rich cultural legacy, proving the power of daydreams and independent thought, among other things.

So, in the seasonal spirit of thankfulness — or just because gratitude is good for you any time of year — here are a few brief reasons to appreciate Einstein:

See full text

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?

See full text

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.

See full text

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.

See full text

An artist’s impression of a supernova explosion. Until now, stellar explosions have been considered singular events. Illustration: Courtesy of the European Southern Observatory/M. Kornmesser.

Star has exploded in ‘fatal’ supernovae multiple times since 1954 – and is the first star astronomers have witnessed doing so

Astronomers have spotted a “zombie star” that refused to die when massive explosions that are normally considered fatal rocked the heavenly body.

The star, which lies half a billion light years away in the constellation of the Great Bear, has exploded multiple times since 1954, but may finally be on its way to the cosmic graveyard.

It is the first time astronomers have seen the same star explode over and over. Until now stellar explosions, or supernovae, have been considered singular events, the dazzling death throes of stars that have burned up all their fuel.

See full text

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.

See full text