The Milky Way galaxy continues to devour its small neighboring dwarf galaxies and the evidence is spread out across the sky.
A team of SDSS-III astronomers led by Sergey Koposov and Vasily Belokurov of the University of Cambridge recently discovered two streams of stars in the Southern Galactic hemisphere that were torn off the Sagittarius dwarf galaxy. This discovery came from analyzing data from the latest Data Release 8 from SDSS-III and was announced in a paper just released as (arXiv paper #1111.7042) that connects these new streams with two previously known streams in the Northern Galactic hemisphere. There is evidence that the brighter stream boasts stars with more heavy elements such as iron, while the fainter stream appears to be older.
(Image Credit: Sergey Koposov) The image above shows a map of the sky showing the numbers of stars counted in the Sagittarius streams. The colors indicate the distances to the stars identified in the study – stars located in red areas are further away, while stars in the blue areas are closer. The dotted red lines trace out the Sagittarius streams, and the blue ellipses in the center show the current location of the Sagittarius Dwarf Galaxy.
(Image Credit: Amanda Smith) The artist’s illustration above shows the four tails of the Sagittarius Dwarf Galaxy (the red-orange clump on the left of the image) orbiting the Milky Way. The bright yellow circle to the right of the galaxy’s center represents our Sun (not to scale). The Sagittarius dwarf galaxy is on the other side of the galaxy from us, but we can see its tidal tails of stars (white in this image) stretching across the sky as they wrap around our galaxy.
For more details see the full press release at http://www.sdss3.org/press/20111130.fourtails.php