Five billion years ago — give or take — a pair of black holes approached their mutual destruction.
They'd been circling each other for a long, long time, but that was about to end. Gradually spiraling closer together over eons, the process accelerated until they whipped around each other at near the speed of light. Then, in less than 100 milliseconds, they approached, distorted, reached out to each other… and merged.
This was no ordinary event. These were hefty black holes, dozens of times the mass of ordinary stars. When they merged to form an even more massive black hole, they let out a positively colossal blast of energy in the form of gravitational waves that literally shook the fabric of spacetime. The waves of energy expanded outward, dissipating with distance.
Then, on 21 May 2019, those waves passed through our planet. Did you feel it? Probably not; the expansion and contraction of space would've stretched you less than a millionth of the diameter of a proton.
But that was enough for the gravitational wave detectors at LIGO to observe this event, dubbed GW 190521. When astronomers looked at the data, they were in for a surprise: This was by ...