[Orbiting black holes gradually grow closer and merge.]
[Each black hole’s surface is an event horizon, from which nothing can escape – even light.]
[The orbital motion of the black holes warps nearby space-time.]
[Some of this warping stays close to the holes]
[…while the rest travels outward,]
[…weakening as it spreads out in space.]
[These outgoing weak distortions of space are gravitational waves
[…traveling at the speed of light. We may detect the waves passing by Earth.]