UC Irvine TODAY UC Irvine homepage UC Irvine TODAY

UC Irvine TODAY

News

News

Thursday, August 21, 2014

News Release

Email this page to a friend EmailPrinter friendly page PrintShare Share

Milky Way’s spiral arms are the product of an intergalactic collision course

UC Irvine models show dark matter packs a punch

— Irvine, Calif., September 14, 2011 —

UC Irvine astronomers have shown how the Milky Way galaxy’s iconic spiral arms form, according to research published today 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.

About the University of California, Irvine: Founded in 1965, UCI is a top-ranked university dedicated to research, scholarship and community service. Led by Chancellor Michael Drake since 2005, UCI is among the most dynamic campuses in the University of California system, with nearly 28,000 undergraduate and graduate students, 1,100 faculty and 9,000 staff. Orange County’s largest employer, UCI contributes an annual economic impact of $4.2 billion. For more UCI news, visit www.today.uci.edu.

News Radio: UCI maintains on campus an ISDN line for conducting interviews with its faculty and experts. Use of this line is available for a fee to radio news programs/stations that wish to interview UCI faculty and experts. Use of the ISDN line is subject to availability and approval by the university.

computer model
Image by Tollerud, Purcell and Bullock/UC Irvine
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.

Media Contact

Janet Wilson
University Communications
949-824-3969
janethw@uci.edu

Experts available

UCI maintains an online directory of faculty available as experts to the media.
University of California, Irvine
University of California, Irvine - Irvine, CA 92697 : 949-824-5011
Comments & Questions | Privacy & Legal Notice | Copyright Inquiries | © 2014 UC Regents