Two black holes orbit each other, setting spacetime rippling. Objects caught in the waves are slowly drawn inward — until they're swallowed and reappear from afar.
Gravitational waves are ripples in spacetime itself — predicted by Einstein's General Theory of Relativity in 1916. Accelerating masses, such as two black holes orbiting one another, generate waves that propagate at the speed of light, stretching and compressing space and time as they pass.
The strongest sources are extreme cosmic events: merging black holes or neutron stars. In the final seconds before merger, the masses spiral around each other ever faster, emitting a characteristic "chirp" — a wave that rapidly rises in both frequency and amplitude.
By the time they reach Earth, the waves are unimaginably faint — compressing space by less than the radius of an atomic nucleus over a distance of kilometers. Laser interferometers like LIGO and Virgo measure precisely these tiny changes in length between kilometers-long mirrored arms. The first direct detection succeeded in 2015, a hundred years after the prediction.
Gravitational waves open an entirely new window onto the universe — independent of light and electromagnetic radiation. They let us "hear" events that remain invisible to telescopes, and provide direct evidence for black holes, their mergers, and the curvature of spacetime itself.