What are gravitational waves?

In September 2015, scientists witnessed something never seen before: two black holes colliding. Both about 30 times as big as our Sun, they had been orbiting each other for millions of years. A fraction of a second before the crash, they sent a vibration across the universe at the speed of light that was picked up by the LIGO detector.

The collision created gravitational waves that rippled across space and revolutionized our understanding of the universe:

Lesson by Amber L. Stuver, directed by Eoin Duffy. Full lesson at Ted-Ed.