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Wednesday, December 02, 2020

LIGO and Virgo announce new detections in updated gravitational-wave catalog

After several months of thorough analysis, an updated catalog of gravitational wave detections has been released by the LIGO Scientific Collaboration and the Virgo Collaboration.

Written by Anuradha Mascarenhas | Pune | Updated: October 29, 2020 6:50:52 pm
LIGO Scientific Collaboration and the Virgo Collaboration, LIGO gravitational waves, gravitational waves research, new gravitational waves, science news, Indian ExpressThis plot shows the masses of all compact binaries detected by LIGO/Virgo, with black holes in blue and neutron stars in orange. Also shown are stellar mass black holes (purple) and neutron stars (yellow) discovered with electromagnetic observations. See also the interactive version of this figure. [Image credit: LIGO/VIrgo/Northwestern Univ./Frank Elavsky]

Detection of gravitational waves has now become commonplace, only five years after the first detection in September 2015. With 50 gravitational-wave detections, scientists at IUCAA and other institutions have updated and released a new catalog.

After several months of thorough analysis, an updated catalog of gravitational wave detections has been released by the LIGO (Laser Interferometer Gravitational Wave Observatory) Scientific Collaboration and the Virgo Collaboration. The catalog contains 39 new signals from black-hole or neutron-star collisions detected between April 1 and October 1, 2019, which more than triples the number of confirmed detections.

This second updated catalog — Gravitational-Wave Transient Catalog 2 — and companion papers of gravitational-wave (GW) events detected by the LIGO and Virgo gravitational-wave detectors were set to be published in arXiv on October 29.

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The new set includes some interesting systems and enables qualitatively new studies of astrophysical populations and fundamental physics. “What is significant about this catalogue, which lists all the 50 black hole and neutron star binaries discovered so far by LIGO and Virgo, is that it establishes quite firmly now that stellar-mass black hole binaries and their collisions are relatively common in the universe, and that a good fraction of them are heavier than what we earlier thought when our sample was limited mostly to black holes in our own galaxy,” Dr Sukanta Bose, chair of LIGO-India Scientific Collaboration ( LISC), told The Indian Express.

“This provides clues on the properties of the parent stars from which they formed in the first place. A large observation sample helps guard against biases. The LIGO-India detector, which plans to join other detectors in the future in such observations, can help in that pursuit. Almost 100 scientists – especially students and junior researchers – collaborated with their LIGO-Virgo partners to make these discoveries happen and enrich our understanding of some of the densest objects in the cosmos and their origin. What is equally fascinating is that we are using them to test Einstein’s theory of gravity. If there is any deviation from its predictions, chances are that observations like these will reveal them first. So far, we find no evidence to suggest any anomalies,” Dr Bose said.

The sharp increase in the number of detections was made possible by significant improvements to the instruments with respect to previous observation periods, the senior scientist at Inter University Centre for Astronomy and Astrophysics said. These included increased laser power, improved mirrors and the use of quantum squeezing technology. All together, these enhancements resulted in a nearly 60 per cent improvement in the range to which signals can be detected. The detectors were also able to operate without interruption more often than in the past, with an improved duty cycle of around 75 per cent vs 60 per cent.

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With all of these new signals, we can begin to better understand the populations of black holes and neutron stars, scientists said. They also explained that the many signals in the updated catalog can be used to put Einstein’s theory of gravity to the test in more and better ways than before.

This was done by comparing the data against predictions from the theory and constraining possible deviations. The results from multiple signals were combined using new statistical methods to obtain the tightest constraints so far on the properties of gravity in the strong, highly-dynamical regime of black hole mergers. With the new catalog, LIGO and Virgo were also able to directly study the properties of the remnant objects produced during the mergers: by measuring the vibrations of these objects, and by ruling out potential “echoes” after the main signals, LIGO and Virgo confirmed that the remnants behaved as we expect from black holes in Einstein’s theory.

The results reported in the new catalog correspond to only the first six months of LIGO and Virgo’s third observing run. Results from the remaining five months are currently being analysed.

In the meantime, the LIGO and Virgo instruments are undergoing upgrades in preparation for the fourth observing run, for which they will be also be joined by the KAGRA detector in Japan. More exciting discoveries are on the horizon, scientists said.

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