Dwarf galaxies orbiting Andromeda challenge galaxy formation theory

Los Angeles Times : Just more than half of the 27 dwarf galaxies orbiting the Andromeda galaxy have been found to share the same orbital plane. And 13 of those 15 are orbiting in the same direction, much as the planets in our solar system all orbit in the same direction around the Sun. The arrangement was detected by a team led by Rodrigo Ibata of the Strasbourg Astronomical Observatory in France using data from the Pan-Andromeda Archaeological Survey . No currently accepted models for galaxy formation predict such dwarf galaxy behavior. Dwarf galaxies are believed to be the remnants of the material that coalesced into giant galaxies such as the Milky Way and Andromeda, so they are expected to be scattered randomly around their parent galaxies. Of further interest in the arrangement, the 15 plane-sharing dwarf galaxies are also on the plane shared by both the Milky Way and Andromeda. Although that may be coincidental, it may also provide more understanding of the structure of galaxy arrangements.