There's no two without three

On January 4th, 2017, LIGO detected two black holes merging into one. One of the black holes was 32 times the mass of the Sun, while the other was 19 times the mass of the Sun. When they merged, they created a black hole 49 times the mass of the Sun. The coalescence instantly converted 2 solar masses of black hole mass into the energy that rattled spacetime enough to generate the gravitational waves we detected almost 3 billion years after it occurred. (Caltech/MIT/LIGO Lab)

Read also: LIGO Picks Up on the Third Ring

LIGO Scientific and Virgo Collaboration (2017). GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2 Physical Review Letters, 118 (22) DOI: 10.1103/PhysRevLett.118.221101