Astronomers spot new generation stars born near back hole

Using NASA's Chandra observatory, astronomers have seen a new generation of stars spawned near a super-massive black hole at the center of the Milky Way.

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, astronomers said Thursday.

Massive black holes are usually known for violence and destruction, since any nearby material, including stars, would be swallowed.

But these new results indicate immense disks of gas, orbiting black holes at a safe distance, can help nurture the formation of new stars, according to Sergei Nayakshin, lead researcher of the study. The findings will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

This conclusion comes from new clues that could only be revealed in X-rays. Until the finding of 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.

But 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.

In the migration model, the stars formed in a cluster far away from the black hole and then migrated in to form the ring of massive stars. The migration scenario predicts about a million low mass, sun-like stars in and around the ring. In the disk model, the number of low mass stars could be much less.

Researchers used Chandra observations to compare the X-ray glow from the region around Sgr A* to the X-ray emission from thousands of young stars in the Orion Nebula star cluster. They found the Sgr A* star cluster contains only about 10000 low mass stars, thereby ruling out the migration model.

Because the galactic center is shrouded in dust and gas, it has not been possible to look for the low mass stars in optical observations. X-ray data have allowed astronomers to penetrate the veil of gas and dust and look for these low mass stars.

"In one of the most inhospitable places in our galaxy, stars have prevailed," Nayakshin said. "It appears star formation is much more tenacious than we previously believed."

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, the researchers concluded.

Source: Xinhua

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