Closest Known Galaxy Just Discovered
A small galaxy has just been detected as it is being ripped apart and swallowed by the much larger Milky Way. The Canis Major dwarf galaxy, as it is now called, is closer to the center of our galaxy than any previously known.
The discovery, announced today by an international team of astronomers, is further evidence that the Milky Way has built its bulk by mergers and acquisitions. Researchers described the galaxy as a "dismembered corpse."
Canis Major dwarf is, on average, about 25,000 light-years from our solar system and some 42,000 light-years from the center of the Milky Way. This is closer than the previous leader in proximity, the Sagittarius dwarf galaxy, discovered in 1994.
The new galaxy does not look like the Milky Way. Besides containing far fewer stars, it is stretched into a shape quite unbecoming to a regular galaxy. In fact, Canis Major dwarf forms a sort of ring around the Milky Way -- a clue to how its being torn apart and swallowed up.
Astronomers found it by detecting several cool, red stars that are otherwise rare in the Milky Way.
"On galactic scales, the Canis Major dwarf galaxy is a lightweight of about only one billion Suns," said Michele Bellazzini of Bologna Observatory, another member of the team. "This small galaxy is unlikely to hold together much longer. It is being pushed and pulled by the colossal gravity of our Milky Way, which has been progressively stealing its stars and pulling it apart."
The galactic snack may be adding 1 percent more mass to the Milky Way, the astronomers estimate.
The discovery was made using data from the Two-Micron All Sky Survey (2MASS). The cool stars, previously undetectable through the dust of the Milky Way, shine brightly in infrared light.
"It's like putting on infrared night-vision goggles," said Rodrigo Ibata of Strasbourg Observatory. "We are now able to study a part of the Milky Way that has been previously out of sight."
Like other digested galaxies, the Canis Major dwarf will eventually live on only as individual stars. Despite the violent ripping apart of its structure, the odds of any star actually colliding with another during the merger are very slim, scientists say.
The finding will be published in the Monthly Notices of the Royal Astronomical Society.