Milky Way Expected to Survive a Beating

Clara Moskowitz
Staff Writer
SPACE.com

Though the Milky Way is taking a good beating from nearby mini-galaxies that sometimes slam into it, our galaxy is not likely to be destroyed by this process as some scientists had predicted, a new study finds.

Circling around the Milky Way are between 20 and 25 known satellite dwarf galaxies, which are smaller clumps of stars bound in orbit around the Milky Way by gravitational attraction.

Some pessimists predicted the Milky Way was doomed to a grizzly death by dismemberment if enough of these galaxies collide with it. In fact, scientists think many satellite galaxies have already rammed into the Milky Way, though so far it has endured.

A new computer simulation indicates that rather than tearing apart a galaxy, collisions with dwarf galaxies serve to puff up the host's pancake-shaped galactic disk. Indeed, evidence of this puffiness has been found in the form of rings and flares of stars around the edges of other galaxies' disks.

"Our simulations showed that the satellite galaxy impacts don't destroy spiral galaxies — they actually drive their evolution, by producing this flared shape and creating stellar rings — spectacular rings of stars that we've seen in many spiral galaxies in the universe," said study leader Stelios Kazantzidis, an astronomer at Ohio State University.

Though our galaxy may not be in danger from dwarf galaxies, astronomers do expect it to eventually collide with the nearest full-size galaxy, Andromeda. In a few billion years, the two spirals should smash into each other head on.

"The collision with Andromeda is a collision between two essentially equal-mass galaxies, whereas satellite bombardment involves encounters with much smaller systems compared to the Milky Way," Kazantzidis told SPACE.com.

Luckily, even that fender bender doesn't necessarily spell the end for the galaxies' inhabitants. Stars are generally spaced wide enough apart within the galaxies that after the merger, most individual stars should intermingle without actually crashing into each other.

In fact, the merging will likely set off a firestorm of new star formation, adding to the richness of the two melded galaxies.

The new simulation helps scientists understand how smaller collisions affect a galaxy's development.

"We can't know for sure what's going to happen to the Milky Way, but we can say that our findings apply to a broad class of galaxies similar to our own," Kazantzidis said.

The model is the most detailed to date of collisions between spiral galaxies and satellites. It revealed the kind of detailed features that should result from these impacts, which align well with observed characteristics of other galaxies seen in the universe.

"Every spiral galaxy has a complex formation and evolutionary history," Kazantzidis said. "We would hope to understand exactly how the Milky Way formed and how it will evolve. We may never succeed in knowing its exact history, but we can try to learn as much as we can about it, and other galaxies like it."

The research is detailed in two papers published in the Astrophysical Journal in August 2009 and November 2008.