November 24, 2008

Collisions helped form disk galaxies

Violent intergalactic collision created the bright pinwheels and broad star sweeps typical in disk galaxies such as the Milky Way, U.S. researchers found.

The multiinstitutional team's simulated galaxy formation suggests disk galaxies likely began as flat, centralized star clusters, the University of Pittsburgh, one of the institutions, said in a news release. Smaller galaxies ripped through these disks billions of years ago, casting disk stars outward into the galaxies' current shapes, their research found.

In addition, huge bodies of dark matter -- a low-density, high-gravity invisible mass -- moved through the disks, pulling stars from the core, researchers said.

Our model suggests that a violent collision throws stars everywhere and continues moving through the disk, disturbing its structure, said Andrew Zentner, a Pitt professor of physics and astronomy. It also has been known for some time that for star spirals to develop and maintain their well-known form, there must be a prolonged disturbance. We show that large masses moving through a galaxy could provide that disturbance.