Astrophysicists working for the Sloan Digital Sky Survey (SDSS) have discovered a new galaxy, so close to the milky way that we could not see it. It’s a dwarf galaxy, but still, it’s currently being cannibalized by the Milky Way. It’s really a case of the trees blocking the view of the forest. You can read the entire press release, if you really want it.
A huge but very faint structure, containing hundreds of thousands of stars spread over an area nearly 5,000 times the size of a full moon, has been discovered and mapped by astronomers of the Sloan Digital Sky Survey (SDSS-II).
At an estimated distance of 30,000 light years (10 kiloparsecs) from Earth, the structure lies well within the confines of the Milky Way Galaxy. However, it does not follow any of Milky Way’s three main components: a flattened disk of stars in which the sun resides, a bulge of stars at the center of the Galaxy and an extended, roughly spherical, stellar halo. Instead, the researchers believe that the most likely interpretation of the new structure is a dwarf galaxy that is merging into the Milky Way.
The new dwarf galaxy is found toward the constellation Virgo.
“Some of the stars in this Milky Way companion have been seen with telescopes for centuries,’” explained Princeton University graduate student Mario Juric, principal author of the findings describing what may well be our closest galactic neighbor. “But because the galaxy is so close, its stars are spread over a huge swath of the sky, and they always used to be lost in the sea of more numerous Milky Way stars. This galaxy is so big, we couldn’t see it before.”
The result was presented today in a session on The Milky Way at the American Astronomical Society meeting in Washington, D.C.
The discovery was made possible by the unprecedented depth and photometric accuracy of the SDSS, which to date has imaged roughly one-quarter of the northern sky. “We used the SDSS data to measure distances to 48 million stars and build a 3-d map of the Milky Way,” explained Zeljko Ivezic of the University of Washington, a co-author of the study. Details of this “photometric parallax” method – using the colors and apparent brightnesses of stars to infer their distances — are explained in the paper “Milky Way Tomography” submitted to The Astrophysical Journal. It is available in preprint form at http://www.arxiv.org/abs/astro-ph/0510520.
“It’s like looking at the Milky Way with a pair of 3-d glasses,” said Princeton University co-author Robert Lupton. “This structure that used to be lost in the background suddenly snapped into view.”
The new result is reminiscent of the 1994 discovery of the Sagittarius dwarf galaxy, by Rodrigo Ibata and collaborators from Cambridge University. They used photographic images of the sky to identify an excess of stars on the far side of the Milky Way, some 75,000 lightyears from Earth. The Sagittarius dwarf is slowly dissolving, trailing streams of stars behind it as it orbits the Milky Way and sinks into the Galactic disk.
January 11th, 2006 | General Science