It's a dog-eat-dog world in intergalactic space.University of Virginia astronomers recently discovered that the Milky Way galaxy is slowly consuming multiple neighboring galaxies in a cosmic battle where size matters most.
In a paper to be published in the December 20 issue of the Astrophysical Journal, the astronomers show that, in what may be a common occurrence in the universe, the Milky Way galaxy is eating up the nearby Sagittarius dwarf galaxy.
As Sagittarius orbits around the more massive Milky Way, the gravity of the larger galaxy pulls stars towards it."You get too close to the center of the galaxy and tidal forces tear you apart," said University Astronomy Prof. Mike Skrutskie, a co-author of the study.
The lead author of the story, University Astronomy Prof. Steven Majewski, originally thought up the idea of intergalactic cannibalism during research he conducted for his Ph.D.The accepted theory said galaxies formed during a discrete period of time and should thus be internally consistent. His work, however, showed that the outer part of the Milky Way was spinning in the opposite direction of the inner part.
While many astronomers who reviewed his work attributed the inconsistency to incorrect calculations on his part, Majewski believed the prevailing model of galaxy genesis was inaccurate.
One day in the summer of 2002, Majewski walked into Skrutskie's office to talk about his theory.
Skrutskie pulled up some data from the recently completed database of the Two-Micron All Sky Survey, for which he was the principal investigator, and searched for stars similar to those found in Sagittarius. The two astronomers produced an image showing large, infrared bright M-giant stars -- which are uncommon in the Milky Way -- forming a tail behind the Sagittarius dwarf galaxy as it orbited around the Milky Way.
They believed that the stars in the tail may have been pulled away from Sagittarius by the Milky Way's gravity. Thus began their work using the 2MASS database, which is the first all-sky survey in the infrared spectra.
The astronomers conducted a more extensive search and analysis of the 2MASS database for stars of the type contained in the dwarf galaxy.
They noticed concentrations of M giant stars common to Sagittarius in and around the Milky Way in a pattern consistent with their theory on the Milky Way consuming Sagittarius.
The proximity of Sagittarius, as well as the motion and spectrum of the anomalous stars, led the astronomers to the conclusion that the Milky Way is devouring Sagittarius.
As a result of the Milky Way's feeding frenzy, stars from Sagittarius have been incorporated into our galaxy.
"They're alien stars, but they're now part of the Milky Way," Majewski said. These alien stars are quite near our solar system -- in astronomical metrics. A star from Sagittarius may be a mere 50 light years away, according to Skrutskie.
Dark matter from the dwarf galaxy, however, may be passing through the Earth right now.
Dark matter is a little-understood form of matter that is not directly observable and only known to exist due to unexplained gravitational forces in many parts of the universe.
"Dark matter from Sagittarius is streaming through here right now," Skrutskie said.
While intergalactic cannibalism may be common -- astronomers have found evidence of the Milky Way consuming two additional dwarf galaxies -- those of us living on Earth aren't at risk of being consumed by another galaxy any time soon, according to Skrutskie:
"There's no giant galaxy waiting to consume our own."
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