MIT scientists have more evidence that black holes
can spin, creating a whirlpool in the fabric of space that pumps
energy out of the black hole and into the region.

Jon Miller, a doctoral candidate at MIT’s Center for Space Research,
led the observation and analysis of a black hole in the Milky Way. He
discusses the findings today (April 22) at the joint meeting of the
American Physical Society and the High Energy Astrophysics Division
of the American Astronomical Society in Albuquerque.

Although matter and light cannot escape black hole XTE J1650-500,
energy manages to vent in the form of rotational energy from the
spin. Like energy released from a flywheel, this surge of power,
conducted along magnetic field lines, brightens the innermost ring of
matter orbiting the black hole before it takes its final plunge into
the mysterious void.

The observation was made with the European Space Agency’s (ESA)
XMM-Newton X-ray satellite.

One striking aspect of the observation, the scientists say, is that
XTE J1650-500 – a stellar black hole with the approximate mass of 10
suns located about 26,000 light years from Earth – behaves nearly
identically to a 10-million-solar-mass black hole over 100 million
light years away in galaxy MCG-6-30-15, as reported in October 2001.
This indicates that black holes have profound similarities in the
manner in which they accrete matter, regardless of their mass.

“As strange as it sounds, it is very likely that black holes spin,
and this has consequences for the matter orbiting and falling into a
black hole,” said Miller. “The fabric of space itself can be dragged
along by the spinning black hole, so matter zips around the black
hole on something analogous to a moving walkway at an airport.”

Scientists have long thought that black holes spin, just like stars
and galaxies, yet they have been hard-pressed to find evidence. After
all, a black hole is a singularity, a point of infinite density
surrounded by a border known as an event horizon, from which no light
can escape.

When a black hole is spinning, matter (usually in the form of
extremely hot plasma glowing predominantly in X-rays) can maintain a
stable orbit six times more closely than it could around a
non-spinning black hole.

With XMM-Newton, Miller’s team observed the spectrum of plasma
orbiting around XTE J1650-500. An emission line from iron in the
spectrum, which would appear as a spike in a more docile setting, was
smeared, pulled towards lower energies. This is called gravitational
redshifting, the result of the black hole’s extreme gravity tugging
on photons (particles of light) and draining their energy as the race
away from the region.

Miller said the gravitational redshifting in XTE J1650-500 was
particularly pronounced, evidence that the matter was extremely close
to the black hole and thus evidence that the black hole was spinning,
allowing matter to orbit so closely.

“Photons escaping out of the gravitational well lose some energy no
matter what,” said Miller. “It’s like climbing stairs. But when the
black hole is spinning, it’s like trying to climb up the ‘down’

Furthermore, the photons, which should appear dim from extreme
gravity sucking their energy, were actually brilliant. Apparently the
matter orbiting the black hole is getting energized from the black
hole itself.

“A spinning black hole possesses a tremendous amount of energy, just
like a rapidly spinning fly-wheel,” Christopher Reynolds of the
University of Maryland, College Park. “We believe that matter in the
immediate vicinity of the black hole can tap into the black hole’s
spin energy and become highly energized. This process occurs because
magnetic fields connect the orbiting gas to the rapidly rotating
space-time. It is incredibly exciting that we are now seeing this
phenomenon in black holes that have widely different masses and
environments. It suggests that energy extraction from spinning black
holes may be much more generic than we previously realized.”

The scientists also relied on data from NASA’s Rossi X-ray Timing
Explorer and the Chandra X-ray Observatory. A paper summarizing this
result has been accepted for publication as a Letter to the May 10,
2002 issue of the Astrophysical Journal. The authors are Jon Miller,
Rudy Wijnands and Walter Lewin of MIT; Andrew Fabian of the
University of Cambridge; Christopher Reynolds; Matthias Ehle of ESA,
Michael Freyberg of the Max Planck Institute; Michiel van der Klis of
the University of Amsterdam; and Celia Sanchez-Fernandez and Alberto
Castro-Tirado of LAEFF-INTA.

For images, refer to