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NEWS RELEASE

02-13-01

Contacts:
Curt Struck, Physics and Astronomy, (515) 294-3666
Skip Derra, News Service, (515) 294-4917

ROLE OF GALACTIC COLLISIONS EXPLORED AT AAAS SYMPOSIUM

AMES, Iowa – Our Milky Way galaxy is cruising through space towards the Andromeda galaxy and the two will collide causing some celestial fireworks. But don't worry. It isn't going to happen any time soon and when it does, the Earth -- given it's relative size and inconspicuous existence -- most likely will be unscathed, said Curt Struck, an Iowa State University professor of physics and astronomy.

Struck and astronomers from around the world will present extensive new research on galaxy collisions, including the collisional history and future prospects within "local groups" of galaxies. They will make their presentations at the 2001 annual meeting of the American Association for the Advancement of Science, Feb. 15 - 20, in San Francisco.

The symposium, "Building the Galactic Neighborhood: Galaxy Collisions in Local Groups," will be 3-6 p.m., Feb. 17. Each speaker will discuss galactic collisions within the local group. Topics include theory and observations of the role of collisions, nearby collisional galaxy groups and the view of a colliding galaxy from a solar system. Struck, who will speak about what a galactic collision might look like from Earth, helped organize the symposium with fellow ISU astronomer Lee Anne Willson.

Astronomers have found that galactic collisions help generate intense rates of star birth and thus represent a fundamental process in the life of galaxies. By studying the structural details of specific types of galaxies, astronomers now believe that galactic collisions play an important role in the evolution and current form of the Universe.

"We have found that collisions in local groups are a very important piece in the big puzzle of galaxy evolution," Struck said.

Our "local group" of galaxies includes a couple of large galaxies plus a couple of dozen small galaxies that are gravitationally bound to the Milky Way. Andromeda is a member of our local group.

"The Milky Way galaxy has probably been involved in a number of small collisions in the past, including multiple encounters with the Magellanic clouds," Struck said. "In a cosmically short time, we will have a close encounter with Andromeda."

Galaxies contain billions of stars like our Sun. A collision between two galaxies will involve the interaction of interstellar clouds. Stars would interact primarily through long-rage gravitational forces.

Struck -- with ISU collaborator Phil Appleton -- has studied galaxy collisions by examining Cartwheel galaxies, galaxies that form a characteristic ring-and-spoke shape after a whole galaxy has passed through the center of it. His research has helped determine how enormously large amounts of star birth are stimulated by galaxy collisions.

The Milky Way-Andromeda collision won't happen for another 500 million years. Struck said the two galaxies are in each other's grasp, but Andromeda is about 50 per cent larger than the Milky Way. Currently, astronomers are not sure how the collision might work out.

"There's a lot of space out there," Struck said. "The solar system is a small target, so it's unlikely to be hit by a star or gas cloud from Andromeda. The collisional effects might amount to as little as having a night sky with twice as many stars."

But from a different vantage point the collision could be spectacular.

"If you were viewing it from a companion galaxy, one galaxy diameter away (roughly 30,000 light years) after a direct collision, you might see a second Milky Way, for example, in the form of an elliptical ring subtending about 60 degrees on your sky with a couple dozen 2 to 4 magnitude blue knots around it. Pretty cool," Struck said.

The only hazards to us that Struck can foresee are the remote chances of increases in high energy electromagnetic and cosmic-ray fluxes -- if we get too close to a region of much induced star formation -- or increased comet showers if we suffer a close encounter with a star or a dense gas cloud core.

What he finds more interesting are the long-term consequences to the vitality of the galaxies involved. Looking at these events on a grander scale, Struck said, "such a collision could enlarge the zone in the remnant disk of a participating galaxy that contains enough heavy elements to make future solar systems."

Or it could all go in the opposite direction.

"The radiation around super starbursts could possibly make a 'dead zone' with a radius of thousands of light years," he explained. "It could catalyze stratospheric pollutants that would destroy the ozone layer of habitable planets within that zone.

"Major mergers with super starbursts that ultimately disperse most of the gas and leave behind an early type of galaxy, might not be a very good place to make future solar systems," Struck added. "That is, there would be little interstellar gas left to make stars like the Sun and new solar systems."

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