Massive Black Holes Found Hiding Out in Dwarf Galaxies

Despite their small size, dwarf galaxies may be home to massive black holes, according to a new study that found more than 150 dwarf galaxies exhibiting signs of large black holes at their center.

"These galaxies are comparable in size to the Magellanic Clouds, dwarf satellite galaxies of the Milky Way," said Marla Geha, an associate professor of astronomy at Yale University. "Previously, such galaxies were thought to be too small to have such massive black holes."

Presented at the 223rd meeting of the American Astronomical Society in Washington, DC, the study included the discovery of light patterns emitted by the galaxies indicating the presence of massive black holes. But while the black holes the researchers detected were roughly 100,000 times the mass of the Sun, they were far less dense than those seen in larger galaxies, which can be up to millions - even billions - of times more massive than the Sun.

"We've shown that even small galaxies can have massive black holes and that they may be more common than previously thought," said Amy Reines, a researcher from the National Radio Astronomy Observatory and lead author of the study. "This is really exciting because these little galaxies hold the clues to the origin of the first 'seeds' of supermassive black holes in the early Universe."

At least in the nearby universe, there is a direct relationship between the bulge in a galaxy's center and the mass of its central black hole, indicating that the two may affect each other in terms of growth.

"Finding these small galaxies with massive black holes is an important step toward understanding how galaxies and black holes developed together," Jenny Greene of Princeton University said. "These dwarf galaxies are the smallest known to host massive black holes and can provide clues to how supermassive black holes get started in the first place."

Key to finding out is determining whether the massive black holes began as some kind of remnant of gigantic early stars or something else entirely.

"Getting a good census of dwarf galaxies with massive black holes is an important first step to resolving this question," Reines said.