POSSIBLE MIDSIZE BLACK HOLE , 600 light-years from galaxy M82's center (green cross), got brighter over a three-month period. To its left are three splotches that got dimmer; they are thought to be smallish holes. Image: Courtesy of NASA/SAO/CXC
Astronomy is the science of extremes--the biggest, farthest, oldest, hottest, coldest, densest, emptiest things known to man. But lately it seems that the strangest celestial bodies come in a medium size. Presenting: the midsize black hole.
The textbooks say that black holes fall into two categories: ones with the mass of a star, formed when a dying star implodes, and ones with the mass of a billion or so stars, formed no one knows quite how. Over the past several years, however, astronomers have built up a case for holes with a mass of 100 to 10,000 suns. "They might be a bridge between the ones we know about--the stellar-mass objects--and the ones we think we know about, the supermassive black holes," says Martin J. Ward of the University of Leicester in England.
This article was originally published with the title Hole in the Middle.