Energy from a Black Hole
Energy from a Black Hole There are plenty of black holes that gobble energy.
Now astronomers have spotted one in a distant galaxy that's giving
some of its energy back.
October 23, 2001: Scientists for the first time have seen energy being extracted from a black hole. Like an electric dynamo, this black hole spins and pumps energy out through cable-like magnetic field lines into the chaotic gas whipping around it, making the gas -- already infernally hot from the sheer force of crushing gravity -- even hotter.
Joern Wilms of Tuebingen University, Germany, and an international team of astronomers observed the novel "power tapping" with the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton) satellite by watching a supermassive black hole in the core of a galaxy named MCG-6-30-15. The observation also may explain the origin of particle jets in quasars.
"Never before have we seen energy extracted from a black hole," said co-author Christopher Reynolds of the University of Maryland, College Park. "We always see energy going in, not out."
Scientists say most galaxies, including our Milky Way galaxy, have a supermassive black hole at their core. A supermassive black hole contains the mass of millions to billions of Suns compressed within a region smaller than our solar system. The black hole in MCG-6-30-15, over 100 million light-years from Earth, has the mass of about 100 million Suns.
The team observed the X-ray glow of iron gas traveling about half the speed of light very close to the event horizon of the black hole in MCG-6-30-15 (an "event horizon" is the theoretical border of a black hole). XMM-Newton captured the spectrum, or chemical fingerprint, of this gas. The spectrum, laid out on a graph, resembles an electrocardiogram with its spikes and dips.
Left: Two spectral lines are present at 6.4 keV: the narrow blue line corresponds to X-rays coming from iron that is far away from the black hole, towards the outer parts of the accretion disc. The broad yellow line is the new mystery feature fully revealed by XMM-Newton. Click on the image for a larger version with labeled axes. Image courtesy XMM-Newton mission.
The iron spectrum from MCG-6-30-15 has extremely broad "spikes," an indication of gravity tugging at the particles of light, called photons, and literally stretching the light. MCG 6-30-15's iron line was so broad, in fact, that the bulk of the light must emanate from very close to the black hole, where the force of gravity is the greatest, Reynolds said.
The total energy output, or luminosity indicated by the spectrum, however, was too bright to be powered by gravity and the free fall of matter alone. Some additional power source must exist to boost the luminosity to the observed intensity.
Co-author Mitchell Begelman of the University of Colorado said this finding may be observational evidence of a theory by Professor Roger Blandford, currently at the California Institute of Technology, and Dr. Roman Znajek, when he was at Cambridge University in England, over 25 years ago. According to the theory, rotational energy can be extracted from the black hole as it is braked by magnetic fields.
Begelman said the energy lost in MCG-6-30-15 is transferred to the inner edge of the accretion disk, a flow of gas swirling around and eventually falling into the black hole. The Blandford-Znajek theory implies that energy flows to particle jets emanating perpendicularly from the accretion disk in certain supermassive black hole systems called quasars. MCG 6-30-15 is not a quasar, but Begelman said the theory can still apply because it predicts that the magnetic field might also link to the disk.
Left: The line profile of iron K-alpha from MCG-6-30-15 observed by the ASCA satellite. The emission line is extremely broad, with a width indicating velocities of order one-third of the speed of light. Click on the image for a larger version with labeled axes. Image courtesy NASA's Goddard Space Flight Center.
XMM-Newton, launched from French Guiana by ESA in December 1999, carries three advanced X-ray telescopes with the light-collecting ability to detect millions of sources, far greater than any previous X-ray mission.
The advanced X-ray observing abilities of this satellite made this important discovery about the energy dynamics of black holes possible, and should lead to other exciting discoveries about our cosmos in the future.
Black hole monster in a spin releases energy! -- more information about the discovery, from the European Space Agency (ESA)
ESA's XMM-Newton -- home page
Black Holes -- a tutorial about black holes and accretion disks
Black Holes -- educational links, from NASA's Spacelink
The Anatomy of Black Holes -- a teachers' resource with lots of information
about black holes, including classroom activities. From NASA's
"Imagine the Universe!"
X-Rays - Another Form of Light -- the basics of X-rays from Harvard's Chandra X-ray Observatory home page
Black Holes and Accretion Disks -- A tutorial from the Harvard CXO Field Guide to X-ray Astronomy
Chandra X-ray Observatory Center -- Gateway to the Universe of X-ray astronomy, for journalists, students and scientists.
NASA's Chandra X-ray Observatory marks two years of important discoveries -- A Marshall Space Flight Center press release.
Science@NASA articles about black holes:
Black Hole Snacks -- NASA's Chandra X-ray Observatory has spotted a curious outburst from our galaxy's core -- a sign that the Milky Way's central black hole may be snacking on its neighbors.
New Evidence for Black Holes -- By seeing almost nothing, astronomers say they've discovered something extraordinary: the event horizons of black holes in space.
A Monster in the Middle -- The Chandra X-ray Observatory may have spied a supermassive black hole in the center of the Milky Way Galaxy
Cosmic Bar Codes -- The Chanda X-ray Observatory has peered into the nucleus of a distant galaxy and detected warm gas flowing away from a black hole.
Measuring Spinning Black Holes -- Using data from several NASA satellites, scientists have measured the spins of several black holes, by accurately measuring the size of the last stable orbit of material around the black hole.
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