Sagittarius A* (Sgr A*)

Oct 14, 2005 16:34 GMT  ·  By

NASA's Chandra X-ray Observatory revealed a new generation of stars spawned by a super-massive black hole at the center of the Milky Way galaxy. This novel mode of star formation may solve several mysteries about these super-massive black holes that reside at the centers of nearly all galaxies.

"Massive black holes are usually known for violence and destruction," said Sergei Nayakshin of the University of Leicester, United Kingdom. "So it's remarkable this black hole helped create new stars, not just destroy them."

Black holes have earned their fearsome reputation because any material, including stars, that falls within their "event horizon" is never seen again. These new results indicate immense disks of gas, orbiting many black holes at a safe distance from the event horizon, can help nurture the formation of new stars. This conclusion comes from new clues that could only be revealed in X-rays. Until the latest Chandra results, researchers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers.

The stars orbit less than a light year from the Milky Way's central black hole, which is known as Sagittarius A* (Sgr A*). At such close distances to Sgr A*, the standard model for star forming gas clouds predicts they should have been ripped apart by tidal forces from the black hole. Two models, based on previous research, to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form.

The research suggests the rules of star formation change when stars form in the disk surrounding a giant black hole. Because this environment is very different from typical star formation regions, there is a change in the proportion of stars that form. For example, there is a much higher percentage of massive stars in the disks around black holes.

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