Coming up with an explanation will be challenging. Andromeda was the only galaxy close enough to make the observation possible. But researchers would like to find more of these extended rings.
Larger numbers would provide increasingly rigorous real-world tests of any explanations scientists devise, notes Chris Stoughton, an astronomer at the Fermi National Accelerator Laboratory in Batavia, Ill., who was not a member of the team that discovered the ring.
In particular, he says, an understanding of these structures could help researchers unravel the mysteries of dark matter – a form of matter that provides the cocoons in which galaxies form and grow, as well as the scaffolding along which galaxies are distributed in the cosmos.
Dark matter earned its "dark" label because it emits no light or any other form of directly detectable radiation. Its presence is inferred by its gravitational effect on the matter astronomers can see.
**The team discovering the rings – led by Rodrigo Ibata of the Strasbourg Astronomical Observatory in France and Geraint Lewis at the University of Sydney in Australia – identified 27 dwarf galaxies in all orbiting Andromeda, also called M31. Thirteen of the dwarf galaxies shared a common orbital plane around Andromeda, and one was offset from the plane of M31's spiral arms by a significant degree.
Other teams had seen hints of the structure in the past, but this new work appears to build the most convincing case.