Two black holes, which at one point were very far apart have merged into a massive black hole.
As a result, astronomers said that they detected a third ripple in the fabric of space-time, a crash that happened 3 billion years ago.
These invisible waves are known as gravitational waves.
Gravitational waves are ripples in the curvature of space-time that propagate as waves at the speed of light, generated in certain gravitational interactions that propagate outward from their source.