[NYTimes] October 22, 2001 Bright Glow May Change Dark Reputation of Black Hole By JAMES GLANZ
Black holes are windowless cosmic dungeons, ultracompressed objects with gravity so powerful that anything that plummets through their trapdoors - surfaces called event horizons enshrouding each one - is forever lost to the rest of the universe. Scientists believe that not even light beams can escape once they are inside.
Now, a surprising find by astronomers, expected to be announced today, may change that dark reputation. Using an X-ray observatory in orbit around Earth, the astronomers have discovered an intense glow, with the intensity of 10 billion Suns, burning just outside the event horizon of a huge but very distant black hole in the constellation Centaurus.
The discovery indicates, the astronomers assert, that they have seen energy pouring out of a black hole and into the surrounding universe for the first time.
The glow is probably not a sign of radiation seeping out, a process scientists still contend is impossible. Instead, it may be caused by a bizarre kind of friction that the black hole, thought to be spinning at nearly the speed of light, feels against surrounding gases, heating them to tremendous temperatures.
That friction may be a result of magnetic fields, stuck to the event horizon like hair, whipping through the gases, said Dr. Mitchell C. Begelman, an astrophysicist at the University of Colorado who is among the leaders of the new research, which involves American and European astronomers.
"What seems to be happening is that there's an extra energy source very, very close to the black hole, which is a big surprise," Dr. Begelman said. The magnetic fields, Dr. Begelman said, "are sort of applying a clutch to the black hole and slowing it down."
The observations were made by the X.M.M.-Newton satellite, launched late in 1999 by the European Space Agency with heavy involvement by the National Aeronautics and Space Administration. X.M.M. stands for X-ray Multi-Mirror, the type of telescopes on board.
The work was led by Dr. Jörn Wilms of Tübingen University of Germany, Dr. Christopher S. Reynolds of the University of Maryland and Dr. Begelman.
Although the findings are likely to be closely examined and debated by observational astronomers, they are not completely unexpected.
More than 25 years ago, Dr. Roger Blandford and Dr. Roman Znajek of the California Institute of Technology proposed that even more powerful displays in the cosmos, like hot jets of gas propelled at nearly the speed of light from the centers of galaxies, might be powered by magnetic fields stuck to spinning black holes.
Astronomers have been unable to uncover the powerhouses behind those displays; the new work is the first sketchy indication that what is known as the Blandford-Znajek effect may occur in the universe.
"There's a huge amount of energy stored in the spin of the black hole," Dr. Blandford said. "You've got a very good flywheel there."
Dr. Blandford said the satellite observations did not prove his theory, but he called them encouraging. Others, like Dr. Kip Thorne, a Caltech physicist who is noted for, among other work, his early theoretical research on black holes, said the observations could open exotic new realms.
Near the event horizon, space itself is believed to be twisted and swirled around in ways ordinary intuition cannot grasp, Dr. Thorne said.
"So far as I know this is the first time we've had evidence of the interaction of magnetic fields with the tornadolike motion of space near the horizon," Dr. Thorne said. He called the work "a very nice result, with implications for the future of exploring physics near the horizon."
The observations focused on what is believed to be a black hole with a mass about 10 million times as great as that of the Sun, said Dr. Reynolds, who said he did much of his work on the observations while at the University of Colorado. The black hole is at the center of a galaxy roughly 120 million light-years from Earth, Dr. Reynolds said.
The observations focused on atoms of iron in what is called an accretion disk. The disk is believed to consist of material, arranged in a structure something like Saturn's rings, that whirls around the black hole before plunging inside. The material around the black hole is so energetic that the iron atoms emit powerful X-rays in a kind of fluorescence.
The spectrum of the fluorescence, which is affected by strong gravity, let the team gauge the total energy of all radiation emitted from just above the event horizon. While all atoms emit powerful radiation as they are torn from the accretion disk into the black hole, Dr. Reynolds said, the results indicated much more energy than could be accounted for by that effect. "The energy in this extra component is something like 10 billion Suns," he said.
That energy, Dr. Reynolds said, probably comes from the magnetic friction.
Dr. Julian H. Krolik, an astrophysicist at Johns Hopkins University, who was not involved in the work, said there could be other explanations, including the possibility that the magnetic fields somehow allow the plunging material to emit more radiation before falling through the irrevocable trapdoor of the black hole. But whatever the explanation, he said, the findings constitute a major discovery.
"These are indications of previously unimagined forces acting on the innermost regions of material accreting onto black holes," Dr. Krolik said.