Iconic rings and flares of galaxies created by violent, intergalactic collisions

November 21, 2008

The bright pinwheels and broad star sweeps iconic of disk galaxies such as the Milky Way might all be the shrapnel from massive, violent collisions with other galaxies and galaxy-size chunks of dark matter, according to a multi-institutional project involving the University of Pittsburgh. Published in the Nov. 20 edition of The Astrophysical Journal, the findings challenge the longstanding theory that the bright extensions and rings surrounding galaxies are the remnants of smaller star clusters that struck a larger, primary galaxy then fragmented.

The study's team consisted of Andrew Zentner, a professor of physics and astronomy in Pitt's School of Arts and Sciences; James Bullock, a physics and astronomy professor at the University of California at Irvine; Stelios Kazantzidis, a postdoctoral researcher at Ohio State University; Andrey Kravtsov, a professor of astronomy and astrophysics at the University of Chicago; and Leonidas Moustakas, a researcher at the NASA Jet Propulsion Laboratory, California Institute of Technology.

The team's computer simulations of galaxy formation suggests that disk galaxies most likely began as flat, centralized star clusters. Smaller galaxies collided with and tore through these disks billions of years ago, casting disk stars outward into the wild extensions present now; the bright center is the original formation. In addition, vast bodies of dark matter—a low-density, high-gravity invisible mass thought to occupy nearly one-quarter of the Universe—swept through these disks and further pulled stars from the main disk.

The researchers' scenario largely applies to the formation of the rings and long flares of stars that surround such galaxies as the Milky Way, Zentner said. But the model also presents a possible solution to how star spirals—the arcs of stars that radiate from the center of some disk galaxies—maintain their shape. Spirals form as a result of any disturbance to the star disk, Zentner said. However, the prolonged disturbance of a galaxy and dark matter expanse passing through a disk explains why the spirals seem to never recede.

"Our model suggests that a violent collision throws stars everywhere and continues moving through the disk, disturbing its structure," Zentner said. "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."

The team's findings were serendipitous, Zentner explained. They were modeling disk galaxies for an unrelated astrological survey when they inadvertently discovered that stars in the main disk scattered when satellite galaxies—smaller galaxies surrounding larger ones—passed through. They shared their results with colleagues a year ago, and the results have since been replicated, Zentner said.

"One of the major advantages of these results is that we didn't set out to find them," he said. "They happened as we simulated existing galaxies."

Source: University of Pittsburgh

Explore further: Dark matter packs a punch: Milky Way's spiral arms formed by intergalactic collision

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rcramer2001
2 / 5 (1) Nov 21, 2008
I'm betting the spirals in spiral galaxies are probably due to frame dragging. Why hasn't anyone else ever seen something so seemingly obvious? By all accounts Spirals have a super massive black hole at their cores, so there has to be frame dragging on a massive scale as well, yes? Einstein B proved frame dragging exists so... if I'm wrong will someone please enlighten me? thanks
smiffy
5 / 5 (1) Nov 22, 2008
How does the symmetrical radial arms of many spiral galaxies fit in with presumably randomly orientated collisions?
smiffy
5 / 5 (1) Nov 22, 2008
I'm betting the spirals in spiral galaxies are probably due to frame dragging. Why hasn't anyone else ever seen something so seemingly obvious? By all accounts Spirals have a super massive black hole at their cores, so there has to be frame dragging on a massive scale as well, yes? Einstein B proved frame dragging exists so... if I'm wrong will someone please enlighten me? thanks


Wouldn't frame-dragging exacerbate the 'winding' problem? And why should distinct arms appear when the frame-dragging effect should presumably be of a uniform nature?
TimESimmons
1 / 5 (3) Nov 22, 2008
Spiral arms are caused by the surrounding anti-gravity matter and Newtonian dynamics - along with most other galaxy features - core and disk, reverse spirals, molecular clouds, globular clusters etc.

http://www.presto...ndex.htm
yyz
1 / 5 (1) Nov 27, 2008
Add this finding to the growing body of evidence supporting the "bottom-up" theory of galaxy formation.

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