Oct. 23, 2001 For the first time ever, astrophysicists have observed extra energy escaping from the supermassive black hole at the center of a distant galaxy.
Undertaken with the European Space Agency’s XMM Newton satellite and an international team of researchers, the study indicates the black hole is spinning, emitting energy through a tangled web of magnetic field lines into the super-hot gases whirling slightly more slowly around it. The gas then becomes even hotter.
"The magnetic field lines are like a series of cable-like strands twisted and tightened around the black hole by intense gravity," said chief study author Joern Wilms of Tuebingen University in Germany. "Our results indicate the X-ray emissions from gas connected to the magnetic field lines are much stronger and much closer to the black hole than we expected."
A paper on the subject has been accepted for publication in the Monthly Notices of the Royal Astronomical Society in London.
"What’s really new here is evidence of additional energy coming from the spin of the black hole," said University of Colorado at Boulder Professor Mitchell Begelman of the astrophysical and planetary sciences department, a co-author on the paper. "The web of magnetic field is imposed on the black hole from the gases around it, slowing its spin."
Begelman, also a member of JILA, a joint University of Colorado-National Institute of Standards and Technology center housed on campus, likened the magnetic field to a truck clutch being let out to slow the vehicle’s speed while traveling downhill. The friction from the clutch helps brake the vehicle, just as the magnetic strands originating from the outer gaseous disk tighten around the black hole, creating friction and slowing its spin.
Christopher Reynolds, now an assistant professor at the University of Maryland at College Park and a paper co-author who worked on the study while a researcher at CU-Boulder, said the only way to explain the compact X-ray energy being observed is that the supermassive black hole is spinning.
"We would expect to see X-ray emissions distributed over a large area if they were produced by the release of gravitational energy from infalling matter into the black hole," he said. "But the big surprise is that the vast majority of these X-rays are coming from a concentrated source in the rapidly rotating disk surrounding the black hole."
Black holes are collapsed objects so tightly compacted that not even light can escape their gravitational pull. Although scientists at NASA’s Goddard Space Flight Center showed recently that small, stellar black holes believed to pepper the universe have the ability to spin, this is the first evidence that supermassive black holes also spin.
Wilms said the supermassive black hole -- known as MCG -6-30-15 and lying more than 100 million light-years from Earth -- contains material roughly equal to between one million and 10 million suns compressed into a piece of the universe much smaller than our solar system. Wilms completed a portion of his doctoral thesis at CU-Boulder under Begelman.
Begelman likened the black hole to a giant battery, storing huge amounts of energy from the constant stream of gas clouds and the occasional stars it gulps up. "It would take roughly a billion years to release all the energy stored up in MCG-6-30-15," he said.
The surprising new findings, linked to the first law of thermodynamics dealing with the conservation of energy, were predicted by scientists 25 years ago who calculated that energy stored in the spin of a black hole could be transferred to surrounding matter.
The theory goes on to predict that some of the energy flows to particle jets shooting perpendicularly from the gas disk in supermassive black hole systems called quasars. The new findings indicate that energy also can be transferred to the inner edge of the gas disk, which eventually falls into the black hole.
Understanding how fast a supermassive black hole is spinning may be an accurate and sensitive probe of how black holes are formed, said Begelman. If one is spinning relatively slowly, it probably has been growing gradually by absorbing individual clouds of gas, stars and much smaller, ordinary black holes formed by single-star collapses.
"But if it is spinning rapidly, it suggests to us that supermassive black holes were formed in a single catastrophic event, perhaps associated with the formation of a galaxy," Begelman said.
The XXM Newton Observatory launched by ESA in 1999 can collect five times as many photons as NASA’s Chandra X-Ray Observatory – which specializes in high-quality digital imagery -- allowing researchers to study the emissions of supermassive black holes in unprecedented detail, said Reynolds. But NASA has several X-ray observatories more powerful than XMM Newton in the construction or planning phase.
Note to Editors: NASA’s still images and movie files, courtesy of NASA’s Dana Berry can be accessed at: http://www.gsfc.nasa.gov/topstory/20011015blackhole.html.
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