Gravitational waves are ripples in the fabric of spacetime caused by the acceleration of massive objects, such as merging black holes or neutron stars. Predicted by Albert Einstein's general theory of relativity in 1915, these waves travel at the speed of light and can carry information about their cataclysmic origins as well as about the nature of gravity. Gravitational waves were first directly detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration in 2015.
