Astronomers clock a black hole spinning at half the speed of light

Oct 2010
This one is difficult to visualize, an object rotating at 93,000 mi./150,000 km per second. But the story is about how the black hole's rotation was determined, not it's speed. Other black holes have been clocked rotating at 99 percent of the speed of light.


Astronomers clock a black hole
spinning at half the speed of light
Black holes are massive beasts that annihilate anything that dares to cross them....​
By observing the X-rays blasting from a star torn apart by a black hole, a team of researchers were able to calculate how fast the black hole spins — clocking it at nearly 50 percent the speed of light. This marks the first time that astronomers used X-rays, which orbit the black hole every 131 seconds, to calculate its incredible speed. The research, which could help correlate a black hole’s age with its speed, was published today in the journal Science.​
The team thinks that these powerful radiation bursts are actually caused by two stars instead of one. The original sighting in 2014 still holds up: a black hole lured in a passing star and tore it to pieces. Some of these stellar shreds, which emit massive amounts of X-ray radiation, were sucked into the black hole. Others, though, remained in the innermost stable circular orbit (ISCO) — the closest spot where objects can orbit a black hole without being devoured by it.​
In that dangerously close orbit lies another star, thought to be a tiny, dense white dwarf. Researchers think that the dwarf’s gravity pulled in the bright stellar remnants, creating a halo of X-rays around it. These X-rays can be seen every time the star orbits the black hole, which is once every 131 seconds.​
They combined the orbital speed of the star with the black hole’s mass, which is thought to be one million time more massive than the Sun, to figure out how quickly the black hole is spinning. According to their calculations, the black hole is rotating at nearly half the speed of light.​
“That’s not super fast — there are other black holes with spins estimated to be near 99 percent the speed of light,” said Dheeraj Pasham, a postdoctoral fellow at MIT and lead author of the paper, in a media release.​

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