Louis J Sheehan 238210.029

Louis J Sheehan Astronomers had speculated that the existence of small, dark matter–dominated satellite galaxies might solve the problem, but there was no evidence that any such galaxies existed.

Last spring, Geha and Josh Simon, a colleague at Caltech, used the 10-meter Keck II telescope on Hawaii’s Mauna Kea to study the mass of eight newly discovered satellite galaxies, detected over the last two years by the Sloan Digital Sky Survey, an ongoing effort to make a detailed map of a million galaxies and quasars. Geha and Simon found that these satellite galaxies were much fainter and smaller in mass than the other known satellites—and 99 percent of their mass was in the form of dark matter. Given that the galaxies found by Geha and Simon have such high concentrations of dark matter, it’s likely that many other satellite galaxies could be 100 percent dark matter.

“We expect some to be undetectable, with no stars or gas,” says Geha. “There are indirect ways of finding the dark matter satellites, but it will take more work.”

Some astrophysicists believe that dark matter particles may occasionally annihilate each other, producing bursts of high-energy gamma rays. If the Milky Way has dark matter satellites, and if they do emit gamma rays, the Gamma-Ray Large Area Space Telescope, scheduled for launch in February, might detect them.

Dark matter may also be responsible for creating the most awesome objects in the universe: the enormous black holes believed to lurk in the center of nearly every large galaxy. Tom Theuns and Liang Gao, astronomers at Durham University in England, used a computer model last year to study how two types of dark matter, known as warm and cold, may have influenced the formation of the very first stars in the universe—and the first giant black holes. HTTP://LOUIS-J-SHEEHAN.US