He was right. From studying the signals emanating from the merging of two black holes — which have separate masses equal to 36 and 29 suns — scientists with the Laser Interferometer Gravitational-Wave Observatory were able to observe gravitational waves. Their measurements matched expectations of what Einstein predicted in his General Theory of Relativity.
The science community spent the past month abuzz with rumors that the scientists from LIGO would make this announcement, but the paper wasn't released until Thursday morning. The study has been published in the Physical Review Letters.
The gravitational waves were caused when the two black holes slowly circled each other in space, losing energy before suddenly colliding. For a quick explainer on how gravitational waves work, watch the video below: