By Elizabeth Landau
(CNN) - 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 show that the spin
rate can be calculated conclusively.
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 at a press briefing
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.
Black holes common in early universe
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.
