GW190521 (or GW190521g; initially, S190521g)[5] is a gravitational wave signal resulting from the merger of two black holes. It was possibly associated with a coincident flash of light; if this association is correct, the merger would have occurred near a third supermassive black hole.[2][6] The event was observed by the LIGO and Virgo detectors on 21 May 2019 at 03:02:29 UTC,[7] and published on 2 September 2020.[4][5][8] The event was 17 billion light years away,[n 1][5][9] within a 765 deg2 area... {open}