Binary black hole

Computer simulation of the black hole merger GW150914. The background is distorted as the intense gravity from the merger causes gravitational lensing.

A Binary Black Hole (often abbreviated BBH), are two black holes in close orbit around each other. The two black holes will eventually merge into one releasing a large amount of gravitational waves.

Discovery

For years the existence of binary black holes was only theoretical. Proving they exist was a challenge due to the nature of black holes. Although if two black holes were to ever merge this would cause a significant amount of gravitational waves to be released. The existence of binary black holes (and gravitational waves themselves) was proven when on September 2015, LIGO detected GW150914.