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

29 October, 2020

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

LIGO Hanford observatory, Photo:LIGO

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 (, a study of astrophysical implications (, tests of general relativity ( and a search for gravitational waves associated with gamma-ray bursts, which has not detected additional signals ( Summaries of the papers will be made available at

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, one of the fastest computers in Europe”, pointed 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).

(part in spanish)

En total cinco grupos en España están contribuyendo a la astronomía de ondas gravitacionales como miembros de las colaboraciones LIGO o Virgo, en áreas que van desde el modelado teórico de las fuentes astrofísicas y el análisis de los datos hasta la mejora de la sensibilidad del detector para los períodos de observación actuales y futuros. Dos grupos, en la Universitat de les Illes Balears (UIB) y el Instituto Galego de Física de Altas Enerxías (IGFAE) de la Universidad de Santiago de Compostela (USC), forman parte de la Colaboración Científica LIGO; mientras que la Universitat de València (UV), el Instituto de Ciencias del Cosmos de la Universidad de Barcelona (ICCUB) y el Institut de Física d’Altes Energies (IFAE) de Barcelona son miembros de Virgo.

El grupo GRAVITY de la UIB es miembro del Instituto de Aplicaciones Computacionales de Código Comunitario (IAC3) de la UIB y del Instituto de Estudios Espaciales de Cataluña (IEEC). Tiene el apoyo del Ministerio de Cienca e Innovación (PID2019-106416GB-I00/AEI/10.13039/501100011033, FPA2016-76821-P), la Vicepresidencia y Consejería de Innovación, Investigación y Turismo, la Dirección General de Política Universitaria y Investigación con fondos de la Ley de Impuestos de Estancias Turísticas (ITS2017-006, PRD2018/24), la Consejería de Educación, Cultura y Universidades del Gobierno de las Illes Balears, el Fondo Social Europeo, el Fondo Europeo de Desarrollo Regional, la Consejería de Innovación, Universidades, Ciencia y Sociedad Digital de la Generalitat Valenciana (PROMETEO/2019/071), de la Red Española de Supercomputación y PRACE. Además, participa en las redes Consolider Multidark (FPA2017-90566-REDC) y Centro Nacional de Física de Partículas, Astropartículas y Nuclear (CPAN- FPA2017-90687-REDC), la red estratégica RED2018-102573-E, la red de excelencia: Red Nacional de Astropartículas (RENATA- RED2018-102661-T) y en varias COST Actions de la Unión Europea (CA18108, CA17137, CA16214 y CA16104).

Información adicional sobre los observatorios de ondas gravitacionales:

La Colaboración Virgo está compuesta actualmente por unos 580 miembros procedentes de 109 instituciones en 13 países diferentes, incluyendo Bélgica, Francia, Alemania, Grecia, Hungría, Irlanda, Italia, los Países Bajos, Polonia, Portugal y España. El Observatorio Gravitacional Europeo (EGO, por sus siglas en inglés) alberga el detector Virgo cerca de Pisa, en Italia, y está financiado por el Centre National de la Recherche Scientifique (CNRS) en Francia, el Instituto Nazionale di Fisica Nucleare (INFN) en Italia, y Nikhef en los Países Bajos. Una lista de los grupos de la Colaboración Virgo puede encontrarse en Más información está disponible en la página web de Virgo:

LIGO ha sido financiado por la National Science Foundation (NSF) y operado por Caltech y MIT, que concibieron LIGO y lideraron el proyecto. El NSF, junto con Alemania (Sociedad Max-Planck), el Reino Unido (Science and Technology Facilities Council) y Australia (Australian Research Council - OzGrav) lideraron el apoyo económico para el proyecto Advanced LIGO, aportando compromisos y contribuciones significativas al proyecto. Aproximadamente 1.300 científicos de todo el mundo participan en las tareas de la Colaboración Científica LIGO, que incluye la Colaboración GEO. Una lista de los colaboradores adicionales está disponible en

Publications & Documents

Related publications of the UIB group

For more details, see, the O3a Catalog detection page on and