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New
discoveries add to understanding of black holes |
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June 7, 2000
WASHINGTON, JUNE 6 (AP) - Supermassive black holes were once only a theory, but astronomers have now found and studied enough of them to draw some conclusions about how they form and where they can exist.
At least 33 supermassive black holes now have been found in the centers of distant galaxies, astronomers reported Monday at a meeting in Rochester, New York of the American Astronomical Society.
John Kormendy of the University of Texas said that it is clear now that big galaxies, with massive bulges of stars around their center, contain huge black holes, some with a mass equal to a billion or more suns. Galaxies
with smaller bulges, such as the Milky Way, the home galaxy
of the sun, contain smaller black holes. The Milky Way's central black
hole is thought to contain a mass equal to about three Kormendy said an analysis also shows that galaxies with stars that are moving more rapidly are more likely to have the biggest supermassive black holes. Stars in a galaxy tend to orbit about the center of the galaxy and the more massive the black hole, the more rapid the motion, he said.
Astronomers also have a better understanding of how black holes formed. Once, there was a question of which came first -- the black hole or the galaxy. Now, said Kormendy, it is clear that black holes and the galaxy around them formed together, with the black holes growing from a diet of gas and stars sucked in from the host galaxy. A black hole is an object in space with such a great mass that it has collapsed under its own gravity. The force of its gravity so intense that nothing can escape, not even light. Thus, the black hole, itself, cannot be seen. Instead, astronomers observe the rapid motion of stars and gas swirling around the black hole. As the matter is accelerated to extremely high speeds, it heats to temperatures and gives streams of electromagnetic radiation. Some black holes have jets of X-rays and gamma rays that move at millions of miles an hour away from the center. Understanding
of black holes has been advanced by observations from
the Hubble Space Telescope, which has identified 10 galaxies with black
holes. The orbiting observatory is able to precisely measure the movement
of gas and stars around a galactic center. From this motion, the mass of
the galaxy's black hole can be calculated.
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