Two black holes merged billions of years ago

Billions of years ago, a collision between two black holes sent gravitational waves rippling through the universe.
The signal detected at LIGO and Virgo resembled “about four short wiggles” and lasted less than one-tenth of a second.
Analysis suggested that GW190521 had most likely been generated by a merger of two black holes.
It was calculated to have come from roughly 17 billion light years away, and from a time when the universe was about half its age.
In the merger leading to the GW190521 signal, the larger black hole was of 85 solar masses.
It is the first “intermediate mass” black hole ever observed.
Merger creates a new black hole of about 142 solar masses. Energy equivalent to eight solar masses was released in the form of gravitational waves, leading to the strongest ever wave detected.
Gravitational waves are invisible ripples that form when a star explodes in a supernova; when two big stars orbit each other; and when two black holes merge.
Travelling at the speed of light, gravitational waves squeeze and stretch anything in their path.
Gravitational waves were proposed by Albert Einstein in his General Theory of Relativity over a century ago.