Astronomers Use Annihilated Star to Clock Black Hole’s Spin
Astronomers have discovered a surprisingly long-lived X-ray pulse from the debris of a shredded star as it inexorably spirals closer to a black hole’s mouth.
The pulse’s timing appears to be tied to the black hole’s spin and indicates that the black hole twirls at a speed at least 50% that of light.
MARK GARLICK/SCIENCE PHOTO LIBRARY / Getty
Spin is one of the fundamental parameters that describe a black hole, like the stats on an ID card. It’s immensely hard to measure; we only have spin measurements for about 30 supermassive black holes, determined