Scientists have been able to pin down the most accurate estimate yet for how fast a supermassive black hole is spinning. The answer is "fast": near the speed of light.
The black hole in question is more than 2 million miles across, with a surface traveling near the speed of light. It is at the center of spiral galaxy NGC 1365 and is the equivalent of about 2 million solar masses. Don't worry, this black hole not an imminent danger to us, given that it's in a galaxy 60 million light years away.
Two instruments helped make these measurements: NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, and the European Space Agency's XMM-Newton X-ray satellite. Scientists used these tools to detect high-energy X-rays to determine the black hole's spin. Although similar measurements have been attempted before, this is the first time scientists have been able to say that they must be correct.
The findings are described in a new study in the journal Nature.
Astronomers found that the spin is at least 84% of the maximum value allowed by Einstein's general theory of relativity. In other words: Einstein was right, again.
"What's amazing in this observation is that we can see the warping and twisting of spacetime, the black hole distorting the very fabric of our universe," NuSTAR principal investigator Fiona Harrison of the California Institute of Technology in Pasadena said Wednesday.
Harrison gave a mind-boggling illustration of what "distortion of spacetime" means: For this particular black hole, if you were standing near the event horizon - the point at which nothing can escape from a black hole - you would be turning around once every four minutes just to stand still.
You may agree with Harrison that "black holes are really weird."
Black holes are dense regions of space that have collapsed in on themselves to the point where not even light can escape the enormous gravitational pull. Still, they are some of the brightest objects in the universe because of the massive amounts of energy released when matter gets eaten by a black hole.
Around a black hole is an accretion disk, dust and gas that's being drawn into the black hole, constantly spiraling toward it. High-energy radiation shines out as the black hole compresses matter. Supermassive black holes in particular are found at the centers of galaxies, including our own Milky Way.
We still don't know how black holes came to be in the first place, but the first seeds were there "just a few hundred million years after the Big Bang," writes Christopher S. Reynolds of the Department of Astronomy and the Joint Space Science Institute at the University of Maryland, College Park, in an accompanying article in Nature.
What we know about how galaxies formed and evolved is closely tied to our understanding of these supermassive black holes, he writes. "The energy released by a growing supermassive black hole can be so powerful that it disrupts the normal growth of the host galaxy; in extreme cases, the AGN (active galactic nucleus) can terminate all subsequent growth of the galaxy."
Black holes start relatively small and get huge over time in one of two ways. They can just keep eating material that falls in; over time, mass accumulates. Or, when two galaxies collide, their black holes can merge into a bigger black hole.
"Measuring the spin is a way to understand how the black hole grew, and this in turn is linked to galaxy evolution," Guido Risaliti, lead study author and astronomer at the Harvard-Smithsonian Center for Astrophysics, told CNN.
The "dream" is to perform these sorts of measurements on galaxies much further away, so that scientists could track the evolution of those structures, too, Risaliti said.
"In order to do this kind of analysis for hundreds of black holes in the very distant universe, we really need the next-generation observatory, a new observatory which would need to be built with much higher sensitivity," Risaliti said.