|
New
Energy Source "Wrings" Power from Black Hole Spin
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 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." "The
gravity in this region appears to be so intense that the very fabric of space
twists around the black hole, dragging magnetic field lines along with it,"
said Wilms. "The magnetic fields tighten about the black hole, slowing its
spin. This 'friction' heats the region to even higher temperatures." 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 black hole in MCG-6-30-15's event horizon, 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. 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, Boulder, said this finding may
be observational evidence of a theory by Prof. Roger Blandford, currently at the
California Institute of Technology, Pasadena, 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. The first law of thermodynamics (conservation of energy) states that energy
lost from the black hole must be absorbed by the region. 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.
ASCA,
a Japanese X-ray satellite, found possible evidence of a spinning black hole in
1994, but the signal was too weak to observe any evidence of energy being extracted
from the black hole. 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. NASA helped fund mission development
and supports guest observatory time. NASA's Goddard Space Flight Center, Greenbelt,
Md., hosts the U.S. guest-observer support center. NOTE
TO EDITORS: MCG-6-30-15 is written as MCG with a "minus sign" in front
of the 6 but a "dash" in front of the 30 and 15. High
Quality Stills from animations: Back
to Top | 
