The Virgo collaboration and the LIGO Scientific Collaboration report the three-detector observation of gravitational waves. This result highlights the scientific potential of a global network of gravitational wave detectors, by delivering a better localization of the source and access to polarizations of gravitational waves.

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The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA and the Virgo detector, located at the European Gravitational Observatory (EGO) in Cascina, near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.

The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The detected gravitational waves – ripples in space and time – were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the Sun and located about 1.8 billion light-years away. The newly produced spinning black hole has about 53 times the mass of our Sun. This means that about 3 solar masses were converted into gravitational-wave energy during the coalescence.

This is the fourth detection of a binary black hole system. While this new event is of astrophysical relevance, its detection comes with an additional asset: this is the first significant gravitational wave signal recorded by the Virgo detector, which has recently completed its upgrade to Advanced Virgo.

It is wonderful to see a first gravitational-wave signal in our brand new Advanced Virgo detector only two weeks after it officially started taking data,” says Jo van den Brand of Nikhef and VU University Amsterdam, spokesperson of the Virgo collaboration. That’s a great reward after all the work done in the Advanced Virgo project to upgrade the instrument over the past six years.

The discovery, accepted for publication in the journal Physical Review Letters (the journal article draft is available for download at these links: and; it will appear tomorrow on arXiv) was made by the LIGO-Virgo Collaboration.

The Virgo detector joined the Network Observing Run 2 (O2) on August 1, 2017 at 10:00 UTC, after the multi-year Advanced Virgo upgrade program, and months of intense commissioning to improve its sensitivity. The real-time detection was triggered with data from all three LIGO and Virgo instruments.  Even though Virgo is at present less sensitive than LIGO, two independent search algorithms based on all the information available from the three detectors demonstrated the evidence of a signal in the Virgo data as well.

The collaboration of LIGO and Virgo has matured over the last decade. Joint collaboration meetings and common data analyses have brought the community together. The coordinated scheduling of observing runs, with all detectors operational, is important to extract the maximum amount of science, and especially the vastly improved source localization holds great promise for the future of multimessenger astronomy. Additional results, based on data from the three-detector network, will be announced in the near future by the LIGO-Virgo collaboration; the analysis of the data is currently being finalized.

GraWIToN project, an Initial Training Network, funded under the FP7 Marie Curie Actions, supported 13 young researchers involved in data analysis and technological developments both in Virgo and LIGO detectors. GraWIToN researchers, recruited by institutions in France, Germany, Italy and the United Kingdom, directly contributed to this scientific achievement that demonstrates the possibility to localize a gravitational wave sources through a network of detectors.

GraWIToN has been a wonderful initiative”, says Michele Punturo, of the Istituto Nazionale di Fisica Nucleare (INFN) and European Gravitational Observatory (EGO), coordinator of the GraWIToN project, “that introduced a team of young researchers in to the gravitational wave research, the youngest and currently most innovative field of research in astrophysics and General Relativity. They directly contributed to exciting discoveries, training themselves to become protagonists of their future research career”.          

The Virgo collaboration

It consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in The Netherlands with Nikhef; the MTA Wigner in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and EGO, the laboratory hosting the Virgo detector near Pisa in Italy.


It is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) 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. Additional partners are listed at




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