A team of astronomers, including two MSU professors, discovered a black hole in an unlikely location.

Stephen Zepf, a physics and astronomy professor at MSU, said the team's discovery of a black hole within a globular cluster, which is a dense collection of stars found in nearly all galaxies, is the first one of its kind.

"The idea of black holes grows directly from Einstein's theory of general relativity," Zepf said in an e-mail. "However, there were various ideas over the years whether a black hole could really exist in nature or not."

A black hole is created when a large star cannot sustain its mass and collapses under its own weight, creating gravity so dense that not even light can escape. Because of this, black holes are completely invisible, making it difficult for astronomers to locate and study them. There is no way to observe a black hole directly, so uncertainty about black holes has been puzzling astronomers for years.

Zepf worked with an international astronomy team made up of Arunav Kundu, a research assistant of physics and astronomy at MSU; Thomas Maccarone, a lecturer at the University of Southampton, England; and Katherine Rhode, a research scientist at Yale University.

"The only way to observe a black hole is when outside matter is falling in," Kundu said. "Because the gravitational force is so intense, the matter heats up, so you can observe X-ray emissions. There is no other astronomical way to explain this emission, besides for a black hole."

The team's interest stemmed from this uncertainty about where black holes could be found.

"Black holes tell us about how the universe evolved and how stars and galaxies were made," Zepf said. "It sheds some light on some fascinating physics."

The team decided to search for a black hole in a globular cluster because their research showed a chance of discovery, and, Zepf said the possibility had not yet been ruled out. The observed galaxy was about 50 million light-years away.

An XMM-Newton telescope was used to make the discovery. A Chandra X-ray telescope was used to make sure the black hole was in the globular cluster, and other ground-based optical telescopes were used to confirm the discovery.

"We were very careful," Kundu said. "We did a lot of tests to make sure that the observation was real. We went through all of the other possibilities that might give us the same result."

The team published the research details online in the Jan. 3 issue of the science journal Nature.

According to Kundu, previous studies said it is highly unlikely for a black hole to be within a globular cluster, making the discovery even more remarkable.

Kundu hopes this discovery may lead to implications on how galaxies evolve and on the early formation of the Milky Way.

"This discovery could make a big difference on studying the evolution of stars," Kundu said.