Binary Black Hole Merger
Illustration of two black holes orbiting each other in a combined accretion disc. Eventually the
black holes will merge, an event that will produce gravitational waves.
Gravitational waves are a prediction of Einstein's theory of general relativity. Gravity is the
distortion of spacetime by mass, and changes in this distortion travel in waves at the speed of
light. The effect is most pronounced where extremely massive objects are subject to extremely high
acceleration. This is seen, for instance, where black holes or neutron stars are in a close orbit
such as this. In February 2016, gravitational waves were detected for the first time, 100 years
after Einstein's prediction. The waves emanated from the collision of two black holes, of 36 and 29
solar masses, some 1.3 billion light years away. The waves were extremely faint by the time they
arrived at Earth, where they were detected by the two LIGO detectors in the USA.