A team of astrophysicists led by Dr Rubens Reis from the University of Michigan has directly measured the spin of a supermassive black hole in a quasar named RX J1131-1231, located 6 billion light years away from Earth.

Multiple images of the quasar RX J1131-1231 are visible in this data from Chandra and Hubble. Image credit: X-ray - NASA / CXC / University of Michigan / R.C. Reis et al; optical – NASA / STScI.

Multiple images of the quasar RX J1131-1231 are visible in this data from Chandra and Hubble. Image credit: X-ray – NASA / CXC / University of Michigan / R.C. Reis et al; optical – NASA / STScI.

Gravitational lensing by an intervening elliptical galaxy – in the middle of the image – has created four different images of RX J1131-1231.

Such lensing offers a rare opportunity to study regions close to the black hole in distant quasars, by acting as a natural telescope and magnifying the light from these sources.

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 scientists, who reported their results in the journal Nature, 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.

The result is important because black holes are defined by just two simple characteristics: mass and spin.

While astrophysicists have long been able to measure black hole masses very effectively, determining their spins have been much more difficult.

These spin measurements can give researchers important clues about how black holes grow over time.

If black holes grow mainly from collisions and mergers between galaxies they should accumulate material in a stable disk, and the steady supply of new material from the disk should lead to rapidly spinning black holes.

In contrast if black holes grow through many small accretion episodes, they will accumulate material from random directions. Like a merry go round that is pushed both backwards and forwards, this would make the black hole spin more slowly.

The discovery that the black hole in RX J1131-1231 is spinning at over half the speed of light suggests that this black hole has grown via mergers, rather than pulling material in from different directions.

Source: http://www.sci-news.com/astronomy/science-rxj11311231-spin-supermassive-black-hole-01795.html