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Milky Way's spiral arms are the product of an intergalactic collision course; Models show dark matter packs a punch

Date:
September 15, 2011
Source:
University of California - Irvine
Summary:
Astronomers have shown how the Milky Way galaxy's iconic spiral arms form, according to new research. A dwarf galaxy named Sagittarius loaded with dark matter has careened twice through our much larger home galaxy in the past two billion years, according to telescope data and detailed simulations, and is lined up to do it again. As the galaxies collide, the force of the impact sends stars streaming from both in long loops.

Computer model of the Milky Way and its smaller neighbor, the Sagittarius dwarf galaxy. The flat disk is the Milky Way, and the looping stream of material is made of stars torn from Sagittarius as a result of the strong gravity of our galaxy. The spiral arms began to emerge about two billion years ago, when the Sagittarius galaxy first collided with the Milky Way disk.
Credit: Image by Tollerud, Purcell and Bullock/UC Irvine

UC Irvine astronomers have shown how the Milky Way galaxy's iconic spiral arms form, according to research published in the journal Nature.

A dwarf galaxy named Sagittarius loaded with dark matter has careened twice through our much larger home galaxy in the past two billion years, according to telescope data and detailed simulations, and is lined up to do it again. As the galaxies collide, the force of the impact sends stars streaming from both in long loops. Those continue to swell with stars and are gradually tugged outward by the Milky Way's rotation into a familiar ringed arm.

It's the weighty dark matter from Sagittarius that provided the initial push, the researchers said.

"It's kind of like putting a fist into a bathtub of water as opposed to your little finger," said James Bullock, a theoretical cosmologist who studies galaxy formation.

The smaller galaxy pays a steep price though -- sucked inward repeatedly by the Milky Way's mightier gravity, it's being ripped apart by the blows, sending huge amounts of its stars and dark matter reeling into the new arms.

"When all that dark matter first smacked into the Milky Way, 80 percent to 90 percent of it was stripped off," explained lead author Chris Purcell, who did the work with Bullock at UCI and is now at the University of Pittsburgh. "That first impact triggered instabilities that were amplified, and quickly formed spiral arms and associated ring-like structures in the outskirts of our galaxy."

The Sagittarius galaxy is due to strike the southern face of the Milky Way disk fairly soon, Purcell said -- in another 10 million years or so.

Additional authors are UCI doctoral students Erik Tollerud and Miguel Rocha, and Sukanya Chakrabarti of Florida Atlantic University in Boca Raton.


Story Source:

The above story is based on materials provided by University of California - Irvine. Note: Materials may be edited for content and length.


Journal References:

  1. Chris W. Purcell, James S. Bullock, Erik J. Tollerud, Miguel Rocha, Sukanya Chakrabarti. The Sagittarius impact as an architect of spirality and outer rings in the Milky Way. Nature, 2011; 477 (7364): 301 DOI: 10.1038/nature10417
  2. Curtis Struck. Astrophysics: Rough times in the Galactic countryside. Nature, 2011; 477 (7364): 286 DOI: 10.1038/477286a

Cite This Page:

University of California - Irvine. "Milky Way's spiral arms are the product of an intergalactic collision course; Models show dark matter packs a punch." ScienceDaily. ScienceDaily, 15 September 2011. <www.sciencedaily.com/releases/2011/09/110914131338.htm>.
University of California - Irvine. (2011, September 15). Milky Way's spiral arms are the product of an intergalactic collision course; Models show dark matter packs a punch. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2011/09/110914131338.htm
University of California - Irvine. "Milky Way's spiral arms are the product of an intergalactic collision course; Models show dark matter packs a punch." ScienceDaily. www.sciencedaily.com/releases/2011/09/110914131338.htm (accessed July 31, 2014).

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