Gravitational waves. Illustration of two neutron stars colliding and emitting 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 high acceleration. This is seen, for instance, where black holes or neutron stars are in a close orbit. In February 2016, gravitational waves were finally detected, 100 years after Einstein's prediction.