A University of Utah astronomer and his colleagues discovered that an ultracompact dwarf galaxy harbors a supermassive black hole -- the smallest galaxy known to contain such a massive light-sucking object. The finding suggests huge black holes may be more common than previously believed. "It is the smallest and lightest object that we know of that has a supermassive black hole," says Anil Seth, lead author of an international study of the dwarf galaxy published in Thursday's issue of the journal Nature. "It's also one of the most black hole-dominated galaxies known."

The astronomers used the Gemini North 8-meter optical-and-infrared telescope on Hawaii's Mauna Kea and photos taken by the Hubble Space Telescope to discover that a small galaxy named M60-UCD1 has a black hole with a mass equal to 21 million suns.

Their finding suggests plenty of other ultracompact dwarf galaxies likely also contain supermassive black holes -- and those dwarfs may be the stripped remnants of larger galaxies that were torn apart during collisions with yet other galaxies.

"We don't know of any other way you could make a black hole so big in an object this small," says Seth, an assistant professor of physics and astronomy at the University of Utah. "There are a lot of similar ultracompact dwarf galaxies, and together they may contain as many supermassive black holes as there are at the centers of normal galaxies."

Black holes are collapsed stars and collections of stars with such strong gravity that even light is pulled into them, although material around them sometimes can spew jets of X-rays and other forms of radiation. Supermassive black holes -- those with the mass of at least 1 million stars like our sun -- are thought to be at the centers of many galaxies.