Black Holes Prevalent, Scientists Find
The universe appears to contain far more black holes than previously known, from ancient monsters lurking in galaxies at the edge of space-time to tiny “naked” holes drifting invisibly through the void. And the exotic objects may have played a crucial role in shaping the visible cosmos.
Those are the conclusions of new research released Thursday from several separate groups of astronomers studying the sky with half a dozen telescopes.
The findings, announced at a meeting of the American Astronomical Society, indicate that “supermassive” black holes--those with masses millions of times greater than the sun’s--are an important, if not essential, part of galaxy formation. In many cases, some astronomers now think, giant black holes formed even before the stars that surround and feed them.
Thus the new observations help to answer “what is the fundamental question in modern astrophysics: How did matter get to be as lumpy as it is?” said Virginia Trimble of UC Irvine, who did not participate in the research.
Black holes form when enormous amounts of matter--anywhere from about three times to billions of times as massive as the sun--collapse to a point. The resulting gravitational field is so strong, and warps space so violently, that it swallows everything within its perimeter, or “event horizon.” Even light cannot escape.
There are, however, a few ways of detecting them. One occurs when neighboring gas and stellar matter swirls into a black hole, forming an “accretion disk” in which the gas is so heated and compressed that it gives off X-rays.
It has been difficult to know how common such objects are. The sky is lighted in all directions with an X-ray glow or “background.” But until recently, instruments haven’t been sensitive enough to discriminate its specific sources.
Thursday, however, astronomers using Chandra, NASA’s newly launched X-ray telescope of unprecedented resolution, announced the discovery that the background radiation comes from myriad individual sources, most of them galaxies presumably containing black holes at their core. One-third of those sources give off no visible light. “There are roughly 100 million [X-ray sources] over the entire sky,” said Chandra scientist Richard Mushotzky of NASA’s Goddard Space Flight Center.
Another group, using data from the Hubble Space Telescope, discovered black holes at the centers of three nearby galaxies, bringing to 20 the number of such objects identified. The apparent ubiquity of the holes implies that “the formation and evolution of galaxies are intimately connected to the presence of a central black hole” in each, said Douglas Richstone of the University of Michigan.
