A Tour of COSMOS Legacy Survey

Narrator (April Hobart, CXC): Scientists have taken major steps in their hunt to find black holes that are neither very small nor extremely large. Finding these elusive so-called intermediate-mass black holes could help astronomers better understand how the largest black holes in the early Universe formed.

The new research comes from two separate studies, each using data from NASA's Chandra X-ray Observatory and other telescopes.

Black holes that contain between about one hundred and several hundred thousand times the mass of the Sun are known as intermediate-mass black holes. This is because their mass places them in between the well-documented and frequently-studied "stellar mass" black holes on one end of the mass scale and the "supermassive black holes" found in the central regions of massive galaxies on the other.

While several possible intermediate-mass black holes have been reported in recent years, astronomers are still trying to determine how common they are and what their properties teach us about the formation of the first supermassive black holes.

One team identified forty growing black holes in dwarf galaxies. Twelve of them are located at distances more than five billion light years from Earth and the most distant is 10.9 billion light years away, the most distant growing black hole in a dwarf galaxy ever seen. One of the dwarf galaxies is the least massive galaxy found to host a growing black hole in its center.

A second team found a separate, important sample of possible intermediate-mass black holes in galaxies that are closer to us. In their sample, the most distant candidate is about 2.8 billion light years from Earth and about 90% of their candidates they discovered are no more than 1.3 billion light years away.This makes them relatively nearby in cosmic terms.

Astronomers are intrigued by intermediate-mass black holes for several reasons, including that they may play a role in the formation of supermassive black holes in the early Universe. They will continue to use Chandra and other telescopes to track these elusive and fascinating objects.