A supermassive black hole at the center of a tiny galaxy is estimated to have a mass of 21 million suns. The mass of the black hole found at the center of our Milky Way galaxy is only about 4 million suns. (Credit: NASA Goddard Space Flight Center/Flickr)

Tiniest galaxy is home to a monster black hole

A huge black hole has been discovered at the center of an ultra-compact galaxy—the smallest galaxy known to contain one.

The findings, published in Nature, suggest that other ultra-compact galaxies also may contain massive black holes—and that those galaxies may be the stripped remnants of larger galaxies that were torn apart during collisions with other galaxies.

Hubble image of two galaxies
This Hubble Space Telescope image compares the size of that galaxy to the gigantic NGC 4647 galaxy. (Courtesy: Michigan State)

There has been much debate whether ultra-compact dwarf galaxies are born as jam-packed star clusters or if they are galaxies that get smaller because they have stars ripped away from them.

The discovery of this black hole, combined with the high galaxy mass and sun-like levels of elements found in the stars, favor the latter idea, says Jay Strader, assistant professor of physics and astronomy at Michigan State University.

The supermassive black hole found at the center of the galaxy known as M60-UCD1 is estimated to have a mass of 21 million suns. By comparison, the mass of the black hole found at the center of our Milky Way galaxy is only about 4 million suns.

The other interesting aspect of this finding is that it suggests supermassive black holes are more common in less-massive galaxies than previously thought, Strader says.

“This means that the ‘seeds’ of supermassive black holes are more likely to be something that occurred commonly in the early universe.”

It continues to be a matter of debate as to whether these black holes could instead have come about as a result of unusual “seeds,” such as “super” stars that collapse directly to massive black holes, or runaway stellar collisions that occurred in the core of a dense star cluster.

The National Science Foundation, the German Research Foundation, and the Gemini Telescope partnership, which includes the NSF and scientific agencies in Canada, Chile, Australia, Brazil, and Argentina, funded the research.

Source: Michigan State University