Evidence for existence of black holes overwhelming
March 11, 1996
The astrophysical evidence for black holes has become so
overwhelming in recent years that astronomers now treat these once-fanciful
objects as normal components of the universe, said a University of Colorado
at Boulder professor.
Mitchell Begelman, professor and chair of the astrophysical,
planetary and atmospheric sciences department, said recent evidence
indicates a staggering number of black holes exist in the universe. They
include the millions of ordinary black holes believed to be peppering each
of the estimated 50 billion to 100 billion galaxies in the universe up to
giant black holes in the centers of most galaxies with masses that are
billions of times greater than the sun's.
Black holes are believed to be regions where gravity is infinite -- so strong that nothing that enters them, including light, can escape,
Begelman said. Containing debris from the collapse of stellar bodies,
black holes "are remnants of stars slightly larger than our sun that used
up their nuclear fuel and died," he said.
Begelman and Martin Rees, Royal Society professor at Cambridge
University, are co-authors of a new book, "Gravity's Fatal Attraction,"
published by the Scientific American Library and distributed by W.H.
Freeman of New York. The 256-page hardcover book, which contains 150
illustrations and photographs, describes the discovery of black holes, the
latest astronomical methods used to detect them and their implications for
the evolution of the universe.
Rees and Begelman are probably the world's leading authorities on the astrophysics of black holes," wrote British scientist
Stephen W. Hawking. "In this clearly written book they explain how stars
with masses a few times that of the sun will inevitably collapse at the end
of their life to form black holes."
Most of the books that have been published on the phenomenon of
black holes were written from a theoretical standpoint, Begelman said.
"One of the things we wanted to emphasize in our book is the astronomical
evidence for these objects and how the recent discoveries of black holes
are driven by new generations of telescopes and new techniques in
astronomy."
The strongest evidence yet is immense clouds containing water vapor that have been observed circling in the center of the galaxy NGC 4258, he
said. By tracking the motion of the water-vapor clouds with powerful radio
telescopes, astrophysicists can chart the gravitational field of the black
hole at the center.
"These telescope observations allow us to see clouds of water vapor
tracing out a disk that is similar in some respects to the disk of our
solar system," he said. "We can plot the speed of particular clouds and
find that they move faster and faster the closer they are to the center,
signaling the existence of a black hole."
Ordinary black holes are relatively small objects, said Begelman.
A black hole with a mass equal that of the sun, for example, would have a
diameter of only about three miles across. In contrast, the sun has a
diameter of about 860,000 miles.
More dramatic are the "supermassive black holes" now believed to
reside at the cores of most galaxies in the universe, he said. "These may
harbor debris from millions to billions of stars that is all tied together
at a single point," he said. "One of the signatures of these 'cosmic
vacuum cleaners' is that they spray jets of gas millions of light years
into space."
Ihe book also addresses how the controversies over black holes and the nature of gravity have contributed to a deeper understanding of
Einstein's theories and exotic objects like quasars and cosmic jets,
Begelman said.
Begelman, who joined the CU-Boulder faculty in 1982, is a former
recipient of a Presidential Young Investigator Award and an Alfred P. Sloan
Foundation Fellowship. He also is a fellow at JILA, a joint institute of
CU-Boulder and the National Institute of Standards and Technology.
Rees, president of the British Association for the Advancement of
Science and a member of the U.S. National Academy of Sciences, holds the
British title of Astronomer Royal. He has held visiting professorships at
Harvard University, the California Institute of Technology and the
Princeton Institute for Advanced Study.
Copies of the book, priced at $32.95, are expected to be available in some Denver-Boulder area book stores, including Barnes
and Noble Book Store in Boulder and the Tattered Cover Book Store in
Denver.
Courtesy of the University of Colorado
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