 The Milky Way
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Nov. 4, 2003 — The Milky Way is colliding with and swallowing up a newly identified galaxy — which is now our galaxy's new nearest neighbor.
An international team including astronomers from the University of Sydney in Australia, the Strasbourg Observatory in France, Bologna Observatory in Italy and Cambridge and Leiceister Universities in England, announced their discovery today. Their research is due to be published within the next few weeks in the Monthly Notices of the Royal Astronomical Society.
The galactic collision between the Milky Way and the dwarf galaxy, named Canis Major after the constellation it is found in, has so far been obscured by dust in the dense disk of the Milky Way.
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A new survey of the sky in infrared light has enabled scientists to see through this dust and pick up M-giant stars — cool red stars that shine brightly under infrared light. The M-giants were used as beacons to trace the shape and locality of Canis Major and to provide a three-dimensional structure of the distant regions of the Milky Way.
"It's like putting on infrared night vision goggles," said team member Rodrigo Ibata of Strasbourg University. "We are now able to study a part of the Milky Way that has previously been out of sight."
Canis Major has a relatively tiny mass of only one billion Suns, and was easy prey to the colossal gravity of our galaxy. It is currently in the process of disintegration as the Milky Way steals its stars. In a spectacular picture the researchers show a pink stream of stars being pulled off the dwarf galaxy by the tidal forces of the Milky Way.
The galaxy is about 42,000 light years away from the center of our galaxy, closer than the Sagittarius dwarf galaxy, our previous closest neighbor, which is also being swallowed by the Milky Way. Canis Major may have added 1 percent of mass to our own galaxy, the researchers said.
Team member, Geraint Lewis of the University of Sydney, said that the findings highlight the relative youth of the Milky Way.
"It is not in its middle age, it is still forming," Lewis said. "It seems that the cannibalized Canis Major galaxy does not only contribute stars to the outer reaches of the Milky Way disk, the pulled-out stream of stars may also pass close to the Sun. These types of interactions could form some of the exquisite detail of our galaxy that we see today."
The researchers have also discovered a new aspect about the formation of galaxies. While astronomers have long suspected that the central part of large galaxies like the Milky Way were built up by swallowing up satellite galaxies that came too close, this is the first time that the outer region — or disk — of a galaxy has been seen doing the same thing.
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