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When Black Holes Merge
By SPACE.com Staff
posted: 07:00 am ET
31 January 2002
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Huge black holes that populated the early universe may have grown by mergers, scientists say, but the details of the process are not well known. A new set of calculations shows how a merger might involve a slow dance lasting up to 10 million years, ending in a violent outflow of energy. The sudden burst could help explain a tendency in the largest black holes -- supermassive objects -- to be either "on" or "off" in terms of their energy emissions. Other researchers have sought clues to this on/off switch. The new study looked at how two merging supermassive black holes, one larger than the other, might be the cause. "It's a violent, very high-energy event," said Priyamvada Natarajan, assistant professor of astronomy at Yale University and one of the authors of an article that will appear in Astrophysical Journal Letters. Philip Armitage, an assistant professor at the University of Colorado, is the paper's lead author. Black holes are dense objects that trap anything that enters them, including light. Astronomers say most large galaxies have one at their centers. Because they can't be seen, black holes are difficult to study, and technically they exist only in theory. They are detected by noting how their incredible gravity affects their surroundings. Any matter spiraling into a black hole does so in a so-called accretion disk, a fairly flat plane of material that surrounds the central object. As the material gets closer, it approaches the speed of light, becomes superheated, and emits X-rays (which is one other way astronomers detect black holes). Some black holes, at the centers of bright galaxies called quasars, are among the most energetic objects known and exist in the distant reaches of the universe, which means they are very old. But not all black holes emit X-rays. The one at the center of our Milky Way Galaxy emits almost none. In the computer simulation, two supermassive black holes become embedded in an accretion disk. They sit quietly at first, then slowly their orbit shrinks, causing them to move closer together, Natarajan said. "What is interesting during this phase is the critical separation stage when the black holes get close enough and all the gas trapped between them immediately rushes to the more massive black hole, leading to a brief increase in brightness coupled with an energetic outflow of gas at very high speeds," she said. MoreBlack Hole News | AstronomyNews Briefs
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