wnol.info July 22 2017


Scientists detect Einstein gravitational waves for a 3rd time

July 22 2017, 10:43 | Guillermo Bowen

Scientists detect Einstein gravitational waves for a 3rd time

Scientists detect Einstein gravitational waves for a 3rd time

The Laser Interferometer Gravitational-wave Observatory has detected its third confirmed black hole merger, and this one's a doozy: LIGO's latest discovery is about 3 billion light-years away, which is more than twice as far away as the first two finds. After waiting for 100 years since the first prediction of the existence of gravitational waves, scientists have detected them three times in the last two years. That's the question that scientists may have answered with this latest discovery, discovering that one of these black holes may have been nonaligned. Misalignment suggests that the black holes formed separately and then came together to create a binary system. But the LIGO team was also able to extract some information about the details of the collision and propagation of gravitational waves.

Maybe that's not as unusual as it sounds.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the US have detected yet another merger of two black holes on January 4, 2017. LIGO's three detections are shown, plus a fourth possible detection that was not strong enough to confirm.

The details of the latest detection, made on January 4 this year, were published today (June 1) in the journal Physical Review Letters.

Today's announcement was made by scientists from the LIGO Scientific Collaboration and the Virgo Collaboration, an worldwide team working to bring a third gravitational wave detector, Virgo, online this summer in Italy.

The detection of a new set of gravitational waves has expanded the window into the universe for scientists - including a team from LSU that has spent the past few years mapping black holes in space, researchers working on the project, who include a team from LSU. And because the gravitational wave arrived undiminished, it provides yet another proof of one of Einstein's theories, showing that gravity travels at light speed. LIGO observations are carried out by twin detectors-one in Hanford, Wash., and the other in Livingston, La. -operated by Caltech and Massachusetts Institute of Technology with funding from the National Science Foundation.

The two identical observatories are L-shaped tubes with a laser running through them. Laser light is reflected by mirrors inside the arms, in an arrangement that can detect distortions in spatial dimensions to an accuracy of less than a thousandth of the width of a proton. David Ottaway, Associate Professor at the University of AdelaideThe most exciting thing about the future of gravitational waves is using detectors limited only by quantum mechanics to measure the composition of neutron stars, which are an exotic form of matter that can not be studied any other way. In the previous two events, the paired black holes seemed to have spins that were aligned.

Further, the LIGO-Virgo team was able, through the new observation, to put tighter constraints on the mass of the graviton, the hypothesized particle that supposedly mediates the gravitational force (analogous to the way that the photon, for example, mediates electromagnetic force).

Stellar-mass black holes are corpses formed when stars more massive than the sun explode and die. The plot had the hallmarks of the accelerating sinusoidal wave that is typical of two objects in the process of merging. The black hole that resulted from the merger had a mass of 48.7 times that of the Sun. But thanks to LIGO's observations, they now know that heavy stellar-mass black holes can exist - probably in cases where the stars have low metallicity.

The first collision resulted in a single black hole with a mass of around 62 times that of our Sun, while the second resulted in a comparative lightweight, coming in at just 21 solar masses.

Image Credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet). And, if they're spinning in the same direction as their orbit, Cadonati said they'd have to shed a bit of this rotational energy before they could merge. That would imply that the black holes were not born together as stars.

Dynamical capture runs counter to a model called "common envelope evolution", in which binary black holes evolve together, with spins that are aligned with their orbital angular momentum. The second detection was made in December 2015. LIGO saw no evidence that the waves travelled at different speeds.

"This new one was a lot farther away than the previous discoveries", Corbitt said. That distance allows us to get more insight into potential deviations from Einstein's theory of general relativity.

"We're starting to gather real statistics on binary black hole systems", Keita Kawabe of Caltech said. The outer contour for each represents the 90 percent confidence region. Outermost curves indicate 90 percent, while inner curves indicate 10 percent.

Astrophysicist Stuart Aston monitors external vibrations on the LIGO test mass mirrors during an engineering run in November 2016. Those sensitivity improvements, said Landry, will extend still further the reach of the LIGO instrument into space; he pointed out that every twofold reduction in LIGO's noise means an eightfold increase in the volume of space that the instrument can query.

What other cool things can we learn from gravitational wave astronomy?

LIGO will detect neutron star mergers and send out an alert to the larger astronomy community, telling researchers to all point their telescopes to that region of sky and catch the event. "We expect that by this summer Virgo, the European interferometer, will expand the network of detectors, helping us to better localize the signals". Detectors are being planned in India and Japan as well.

Within tens of seconds, LIGO's search algorithms automatically analyzed the signal, comparing it to waveforms characteristic of gravitational waves. However, we did not know that at the time and it took me and others in the Collaboration a long time to become confident that the first signal was indeed a gravitational wave.



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