LIGO and Virgo Announce Four New Gravitational-Wave Detections

3 December, 2018


The team of researchers of the UIB has made important contributions to the observation and analysis of the signals detected. The observatories publish the first catalog of gravitational wave events.

On Saturday, December 1, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation's LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European-based VIRGO gravitational-wave detector regarding their searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced.

From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now. The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

UIB contribution

The UIB group, under the leadership of Prof. Alicia Sintes, has made important contributions to the observation and analysis of the detected gravitational wave signals. A key contribution of the UIB group has been to provide models of the gravitational wave signals of binary black hole mergers. Such accurate waveform models are used by the collaboration to compare the observed data to theoretical predictions and are vital in order to characterise the sources of the signals, e.g. the masses and spins of the compact binaries.

Sascha Husa, who has lead the UIB group’s effort to model black holes, says “We spend most of out time with computers and calculations. Seeing how all the hard work reveals new insights about the universe is deeply satisfying. The students and postdocs in our group are being part of a scientific revolution - I am very happy that they can make this very special and rare experience.”

One of the group’s postdoctoral researchers, Dr Geraint Pratten, has been actively involved in the analysis of one of the new BBH detections, GW170809. "It has been an exciting time for the collaboration with so many new detections. GW170809 is one of the heavy stellar-mass binary black hole mergers observed in O2. This event is broadly similar to GW150914 and is helping to provide a more detailed picture of the underlying astrophysical population of black hole binaries that we are now observing." The third observing run (O3) is planned to commence in early 2019 with even more sensitive detectors. Many tens of binary observations are anticipated in the coming year and ever more accurate waveform models will be needed in order to extract as much information as possible from these events.

 Alicia Sintes is excited about the growing Spanish participation in gravitational wave science: “The Spanish gravitational wave community is growing very fast - from being alone three years ago, to now two groups in the LIGO collaboration, and three in the Virgo collaboration. We feel proud to have helped pave the way.” She is also thinking about the next challenges: “Now we are starting to push gravitational wave astronomy further. With the LISA mission we want to observe gravitational waves from space in fifteen years. We are working hard so that some of the students we train now can become the leaders of the field in the future.”

Breaking records detections

All of the events are included in a new catalog, also released Saturday, with some of the events breaking records. For instance, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 9 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

The Advanced Virgo detector joined the second observing run on August 1st, 2017 enabling the first three-detector observation of gravitational waves from a binary black hole, GW170814, marking the first significant event observed by the Virgo detector. The LIGO and Virgo observatories report a new binary black hole three-detector observation, GW170818, highlighting the scientific potential of a three-detector network of gravitational wave observatories.

GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. What's more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

One of the new events, GW170818, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

"The next observing run, starting in Spring 2019, should yield many more gravitational-wave candidates, and the science the community can accomplish will grow accordingly,” says David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “It’s an incredibly exciting time.”

The Collaborations

LIGO is funded by NSF and operated by Caltech and MIT, which conceived and led the Initial and Advanced LIGO projects built the project. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. More than 1,200 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at

The Virgo collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; 11 from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with IFAE and the Universities of Valencia and Barcelona; two in Belgium with the Universities of Liege and Louvain; Jena University in Germany; and the European Gravitational Observatory (EGO), the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef.

A list of the Virgo Collaboration can be found at: More information is available on the Virgo website at