Distant supermassive black hole spins at half the speed of light

By magnifying a region of space 6 billion light-years away, astronomers have directly measured the spin of a distant black hole — and holy crap do these things ever rotate quickly.

The quasar shown above is RX J1131-1231. The striking image was captured by NASA's Chandra X-ray Observatory and the Hubble Space Telescope using a gravitational lensing technique. The extremely luminous quasar is produced by a nearby supermassive black hole that's pulling in surrounding gas.


Black holes are typically measured according to two characteristics: mass and spin. Figuring out mass is relatively easy, but determining spin is another story.

Because of the gravitational lens — which offers a magnified view of a distant region in space — the astronomers were able to get detailed information on the X-ray spectrum — the amount of X-rays seen at different energies. This in turn allowed them to get extremely accurate and unprecedented values for how fast the black hole is spinning.

The Chandra X-Ray Observatory explains:

The X-rays are produced when a swirling accretion disk of gas and dust that surrounds the black hole creates a multimillion-degree cloud, or corona near the black hole. X-rays from this corona reflect off the inner edge of the accretion disk. The reflected X-ray spectrum is altered by the strong gravitational forces near the black hole. The larger the change in the spectrum, the closer the inner edge of the disk must be to the black hole.

The authors of the new study found that the X-rays are coming from a region in the disk located only about three times the radius of the event horizon, the point of no return for infalling matter. This implies that the black hole must be spinning extremely rapidly to allow a disk to survive at such a small radius.


And by rapidly they mean approximately 150,000,000 meters per second. This suggests that the black hole grew via mergers, rather than pulling in material from different directions.

Last year, astronomers calculated the spin of a supermassive black hole the center of spiral galaxy NGC 1365 at a blistering 84% the speed of light. So technically speaking it's not the first direct measurement — but it may be the most accurate.


[ Chandra X-Ray Observatory ]

Image: X-ray: X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI


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