January 16, 2004

The Hungry Universe


Sloan Digital Sky Survey Reveals Giant Clump of Stars Near Andromeda Galaxy

Atlanta -- A international team of astronomers from the Sloan Digital Sky Survey collaboration has discovered a giant clump of stars near the Andromeda Galaxy that could be a previously unknown satellite galaxy of Andromeda or could be the last remnants of a galaxy torn apart by Andromeda's tidal forces.

The clump of stars, named Andromeda NE by the researchers for its location to the northeast of the Andromeda Galaxy, is enormous. It covers a larger area on the sky than the full Moon. If added together the total light from the stars in Andromeda NE would rival many nearby galaxies in brightness. Yet because these stars are so spread out, Andromeda NE appears 10 times dimmer than the faintest known galaxy.


While analyzing data from an SDSS scan of Andromeda, Zucker and his team used special filtering techniques to select objects with specific colors and brightness typical of Andromeda's stars. When the SDSS team mapped the distribution of these stars they detected a number of features previously noted by other astronomers. But SDSS researchers didn't know what to make of a large concentration of stars - what they described at first as a giant, ghostly shape ....

"One of the most important questions about Andromeda NE is its distance. Although our findings don't allow us to measure this precisely, our data indicate that it is roughly at the same distance as the Andromeda Galaxy," said Bell.

That means that the clump of stars is gravitationally bound to the Andromeda Galaxy, in orbit around its larger neighbor and possibly is in the process of being torn apart by Andromeda's tidal forces. These forces arise because Andromeda's gravitational pull is stronger on the near side of Andromeda NE than on the far side, pulling the stars away from each other. "For most small companion galaxies it is ultimately only a matter of time until they are shredded by the tides of the parent galaxy," explained Hans-Walter Rix, director of MPIA.

Over the past decade astronomers have found increasing evidence that the distant, outer reaches of normal spiral galaxies like Andromeda and the Milky Way are not quiet backwaters, but rather arenas of ongoing galaxy disruption. As satellite galaxies are ripped apart by tidal forces, they lose stars in great streams along their orbital paths. Researchers have detected such stellar streams around both the Milky Way and Andromeda, suggesting that this kind of galactic cannibalism is commonplace.

Posted by Vanderleun at January 16, 2004 9:24 AM | TrackBack
Bookmark and Share