Matias Zaldarriaga

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.

A hum resonates across the universe. It is not sound, but a trembling of space itself — the gravitational wave background. It is produced by pairs of supermassive black holes circling each other at the centers of distant galaxies. Each pair is like a bass instrument in a vast orchestra.

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.