Digvijay Wadekar

When black holes collide, the very fabric of spacetime trembles. That rumble, gravitational waves, gets picked up by detectors, but decoding the signal used to take hours of computer simulation.

Black holes come in two types: tiny ones — the remnants of supernova explosions, and giants in the cores of galaxies. But where are the intermediate ones, with hundreds and thousands of solar masses? The answer may lie in star swarms, where black holes collide like balls on a billiard table and, merging, bulk up.

On November 23, 2023, LIGO detectors caught something strange. The gravitational wave signal from a black hole merger, designated GW231123, pointed to record masses—137 and 101 solar masses, and anomalously fast spin. That would be the most massive and fastest-spinning pair ever detected.

Two black holes circle in a cosmic dance, spiraling closer together. In the end, they merge into one, and that moment unleashes a powerful burst of gravitational waves, ripples in spacetime itself. But what remains after the merger?