Two articles published on the arXiv server show a catalog of gravitational wave events detected by the LIGO and Virgo collaborations and the inferred properties concerning the black hole pairs discovered in the mergers. So far, 7 events were announced but the analysis of the data led to the discovery of 4 more events of which one was detected by Virgo as well. Of the 11 now known, there’s the one that became famous because it was generated by two neutron stars that led to a kilonova while the other 10 were generated by black hole pairs.
The astronomy based on gravitational waves has finally been opened thanks to the first detections made by the LIGO experiment in the USA during the run carried out between 2015 and the beginning of 2016 with the discovery of three mergers black hole pairs of which the first was announced in February 2016. This new branch of astronomy was then expanded with the subsequent run, which was joined by the Virgo experiment in Italy in August 2017.
The two collaborations that manage the activities of the two experiments that now include the two LIGO detectors in Louisiana and Hanford and the Virgo detector analyzed the data collected to create a catalog of the events detected. A data processing that’s become more advanced thanks to the accumulated experience allowed to include 4 more black hole merger events indicated as GW170729, GW170809, GW170818, and GW170823. The image (Image courtesy Teresita Ramirez/Geoffrey Lovelace/Sxs Collaboration/LIGO-Virgo Collaboration) shows the scheme of the 10 black hole merger events.
The event GW170729 is the one that occurred at a greatest distance, about 5 billion light years. The researchers estimated that the merger between black holes released an energy equivalent to about five solar masses, converted into gravitational waves. This also makes it the most energetic event identified so far.
The event GW170814 was the first detected by the network consisting of three detectors after the activation of the Virgo experiment and was recorded only three days before GW170817, the most famous of all because generated by the merger of two neutron stars and therefore detected at both gravitational waves and electromagnetic waves, a progenitor of multimessenger astronomy. GW170818 and GW170823 were recorded in the following days.
In spring 2019 the third run of the LIGO and Virgo experiments will begin, with the hope of discovering new gravitational wave events even from different sources. Alessio Rocchi, researcher at the INFN and coordinator of Virgo commissioning, hopes to discover them from pulsars, from systems composed by a black hole and a neutron star and even from supernovae to add neutrino detections, a further messenger. In essence, not only gravitational wave astronomy will become increasingly important, but thanks to it, multimessenger astronomy will also grow.