Churning spacetime and destroyed stars help reveal how fast supermassive black holes spin

In the background, a vibrant pink accretion disk is seen swirling around a black hole's singularity. A trail of orange matter trails behind. An inset in the top right shows a diagram of a black circle spinning.

The "wobbling" remains of a star that suffered a grisly death at the maw of a supermassive black hole has helped reveal the speed at which its cosmic predator spins.

Supermassive black holes are believed to be born through successive mergers of smaller black holes, each of which brings with it angular momentum that speeds up the rotation of the black hole they birth. Consequently, measuring the spin of supermassive black holes can grant insight into their history — and new research offers a new way to make such inferences based on the effect spinning black holes have on the very fabric of space and time.