Ten years ago, humanity recorded gravitational waves consistent with the collision of two black holes, registered in 2015 as a distortion smaller than a fraction of the width of a proton. This past month the LIGO-Virgo-KAGRA collaboration released GWTC-5.0, the fourth Gravitational-Wave Transient Catalog, and the count now stands at roughly 390 confirmed events. In a single decade, a science has been born and brought to a new level. We have moved from simply being able to detect gravitational waves at all to building up a catalogue of observations. The collaboration is international: LIGO operates two facilities in the United States, Virgo operates in Italy under European sponsorship, and KAGRA is in Japan.
With hundreds of black-hole and neutron-star mergers on record, astronomers can ask new questions about the distribution of these events and objects. How are these mergers distributed, how large are the stars, how often do they collide? Does Einstein’s general relativity hold across the cosmos? One event in the new catalog, GW240615, was among the most precisely localized. It pinpointed to within 6 square degrees of sky the merger of black holes some 26 and 30 times the mass of our Sun, more than 3 billion light-years away.