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

The Gravity group at UIB has contributed to the analysis of the 39 new signals detected between April 1 and October 1, 2019 by the LIGO and Virgo detectors

After a highly successful third observing run and several months of thorough analysis, the LIGO Scientific Collaboration and the Virgo Collaboration have released an updated catalog of gravitational wave detections. This new GWTC-2 catalog follows the previous one from the first two observing runs (GWTC-1, published in November 2018), and contains 39 new signals from black-hole or neutron-star collisions detected between April 1—Oct 1, 2019, which more than triples the number of confirmed detections. The new set includes some of the most interesting systems we have seen so far, and enables qualitatively new studies of astrophysical populations and fundamental physics.

A total of four scientific papers will be released simultaneously, presenting the catalog of new sources (https://dcc.ligo.org/P2000061/public), a study of astrophysical implications (https://dcc.ligo.org/P2000077/public), tests of general relativity (https://dcc.ligo.org/P2000091/public) and a search for gravitational waves associated with gamma-ray bursts, which has not detected additional signals (https://dcc.ligo.org/P2000040/public). Summaries of the papers will be made available at https://ligo.org/science/outreach.php.

The sharp increase in the number of detections was made possible by significant improvements to the instruments with respect to previous observation periods. These included increased laser power, improved mirrors and, remarkably, the use of quantum squeezing technology. All together, these enhancements resulted in a ~60% 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 ~75% vs ~60%.

With all of these new signals, we can begin to better understand the populations of black holes and neutron stars in the Universe. By analyzing the entire observed set of binary black hole mergers simultaneously we can maximize the astrophysical information we extract. We infer that the distribution of black hole masses does not follow a simple power-law distribution. Measuring the deviations from this power law will enable us to learn about the formation of these black holes, either as the result of stellar deaths or previous collisions. Considering the entire population together also allows us to make stronger measurements of difficult to measure properties such as black hole spin. We find that some merging black holes have spins which are misaligned with their orbital angular momentum. This will allow us to probe the regimes in which these binaries formed.

We can also use the many signals in the updated catalog 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 analyzed. In the meantime, the LIGO and Virgo instruments are undergoing upgrades in preparation for the fourth observing run, for which they will be also joined by the KAGRA detector in Japan. More exciting discoveries are on the horizon.

The group at the University of the Balearic Islands (UIB) has contributed to these results in various ways: Group leader Alicia Sintes has acted as one of the reviewers of results from the search for gamma-ray bursts, the group has contributed to the development of the theoretical models that are used to decode the properties of the sources in an effort lead by Sascha Husa, along with actively participating in the practical parameter estimation for several of the new events, doctoral student Pep Covas and Rodrigo Tenorio have worked at the Hanford detector site during three months each to characterize the noise of the detector during this run, which is essential to distinguish astrophysical signals from noise created on Earth, and David Keitel has coordinated the outreach summaries for the four new publications. In parallel, the group has been very active in 2020 to publish new, highly efficient models of binary collisions that will allow scientists to study the full symphony of gravitational waves, including its overtones. Until now the overtones of gravitational wave signals have not been used routinely, and in the published catalog systematic exploration of their effects has still been limited due to their high computational cost. The models that the UIB group has presented in 2020 in a total of six publications (two still under peer review) will allow to efficiently and systematically study the overtones for all detected events in this and future catalogs. First studies have already used the new models to refine results for the event GW190412 (originally published in April), in a paper by the UIB group, and to suggest a possible alternative interpretation of the most massive binary black hole merger detected to date (originally published in September), GW190521. The latter work has been conducted by a group at the Albert Einstein Institute in Germany.

“As for everybody else this has been a truly remarkable year for our group, with many ups and downs, and the largest number of scientific publications our group has been able to publish in any year, not counting those of the LIGO collaboration. I am relieved that this catalog is now released, but possibly even more that we have just been granted almost another ten million hours of computing time by the Spanish Network for supercomputing (RES), which allows us to continue our work for another four months at the same level, and study the most interesting event candidates for the next catalog of gravitational waves. “I am particularly grateful to be able to work with the supercomputador Mare Nostrum, on of the fastest computers in Europe”,  says Sascha Husa (UIB).

“It is very difficult for a group in Mallorca to contribute to such a large scale scientific effort, and both collaborate and compete with institutions such as the California Institute of Technology, MIT, or the German Max Planck society with the means we have here, but we are optimistic that Spain will recognize the importance of i+d+i and increase its investment toward a knowledge-based economy”, adds Alicia Sintes, leader of the group at the University of the Balearic Islands (UIB).

Publications & Documents

Related publications of the UIB group

● Towards the routine use of subdominant harmonics in gravitational-wave inference: re-analysis of GW190412 with generation X waveform models
Authors: Marta Colleoni, Maite Mateu-Lucena, Héctor Estellés, Cecilio García-Quirós, David Keitel, Geraint Pratten, Antoni Ramos-Buades, Sascha Husa
https://arxiv.org/abs/2010.05830, October 2020

● IMRPhenomTP: A phenomenological time domain model for dominant quadrupole gravitational wave signal of coalescing binary black holes
Authors: Héctor Estellés, Antoni Ramos-Buades, Sascha Husa, Cecilio García-Quirós, Marta Colleoni, Leïla Haegel, Rafel Jaume
https://arxiv.org/abs/2004.08302, April 2020, submitted to Physical Review D

● Let’s twist again: computationally efficient models for the dominant and sub-dominant harmonic modes of precessing binary black holes
Authors: Geraint Pratten, Cecilio García-Quirós, Marta Colleoni, Antoni Ramos-Buades, Héctor Estellés, Maite Mateu-Lucena, Rafel Jaume, Maria Haney, David Keitel, Jonathan E. Thompson, Sascha Husa
https://arxiv.org/abs/2004.06503, April 2020, submitted to Physical Review D

● Setting the cornerstone for the IMRPhenomX family of models for gravitational waves from compact binaries: The dominant harmonic for non-precessing quasi-circular black holes
Authors: Geraint Pratten, Sascha Husa, Cecilio Garcia-Quiros, Marta Colleoni, Antoni Ramos-Buades, Hector Estelles, Rafel Jaume
https://arxiv.org/abs/2001.11412 January 2020,
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.102.064001 September 2020

● Validity of common modelling approximations for precessing binary black holes with higher-order modes
Authors: Antoni Ramos-Buades, Patricia Schmidt, Geraint Pratten, Sascha Husa
https://arxiv.org/abs/2001.10936 January 2020,
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.101.103014 May 2020

● IMRPhenomXHM: A multi-mode frequency-domain model for the gravitational wave signal from non-precessing black-hole binaries
Authors: Cecilio García-Quirós, Marta Colleoni, Sascha Husa, Héctor Estellés, Geraint Pratten, Antoni Ramos-Buades, Maite Mateu-Lucena, Rafel Jaume
https://arxiv.org/abs/2001.10914, January 2020
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.102.064002, September 2020

● Accelerating the evaluation of inspiral-merger-ringdown waveforms with adapted grids
Authors: Cecilio García-Quirós, Sascha Husa, Maite Mateu-Lucena, Angela Borchers
https://arxiv.org/abs/2001.10897, January 2020
Classical and Quantum Gravity (https://iopscience.iop.org/journal/0264-9381), in print, October 2020

Other Documents:
Science Summary

For more details, see https://www.ligo.org/detections/, the O3a Catalog detection page on ligo.org and https://www.virgo-gw.eu/GWTC-2

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