The Milky Way galaxy possesses a distinct outer halo that orbits in the opposite direction from its inner halo and the rest of the galaxy, researchers say. This second halo contains some of the most primitive stars in the universe, offering new evidence about how the galaxy formed.
Some scientists had previously suspected that a portion of the stars in the Milky Way travel in a different direction from the rest. But data on such stars were too sparse to conclude that an entire second halo existed.
Now, an international team of scientists including Timothy Beers of Michigan State University in East Lansing has discovered stronger evidence for a double halo. Beers and his colleagues analyzed more than 20,000 stars as part of the Sloan Digital Sky Survey, an astronomical effort to create a three-dimensional map of about a million galaxies.