Researchers directly measured the spin of a twirling black hole six billion light years away.
Black holes are defined by their mass and spin. Researchers have known how to measure their mass for some time, but the spin is a little trickier, a NASA news release reported.
In only the past 10 years researchers have been working on a step-by-step approach for estimating the spins of black holes over than several billion light-years away ("meaning we see the region around black holes as they were billions of years ago") the news release reported.
"We want to be able to cut out the middle man, so to speak, of determining the spins of black holes across the universe," Rubens Reis of the University of Michigan in Ann Arbor, who led a paper describing this result that was published online Wednesday in the journal Nature, said in the news release.
The team observed a black hole that is creating a quasar, dubbed RX J1131-1231, by sucking in surrounding gas, A giant elliptical galaxy creates a "gravitational lens" that magnifies the quasar's light.
"Because of this gravitational lens, we were able to get very detailed information on the X-ray spectrum - that is, the amount of X-rays seen at different energies - from RX J1131," said co-author Mark Reynolds also of Michigan. "This in turn allowed us to get a very accurate value for how fast the black hole is spinning."
By measuring the black hole's spin the researchers were able to gain insight into how the objects grow over time. The researchers found RX J1131 is spinning at over half the speed of light; since it is at a distance of six billion light years away from Earth this means it most likely formed about 7.7 billion years after the Big Bang.
The study results suggest the black hole grew from a series of collisions and mergers between galaxies as opposed to "small accretion episodes."
