The Andromeda galaxy, the closest large spiral to the Milky Way, appears calm and tranquil as it wheels through space. But appearances can be deceiving. Astronomers have new evidence that Andromeda was involved in a violent head-on collision with the neighboring dwarf galaxy Messier 32 (M32) more than 200 million years ago.

“Like a CSI team, we gathered clues and reconstructed the scene of the crime,” said Pauline Barmby (Harvard-Smithsonian Center for Astrophysics), a member of the research group that made the discovery. “The evidence clearly shows that M32 is guilty of committing a hit-and-run.”

This discovery was reported in the Oct. 19, 2006, issue of the journal Nature.

Dramatic proof of the galactic smash-up came from images taken by the Infrared Array Camera (IRAC) on NASA’s Spitzer Space Telescope. Those images revealed a never-before-seen dust ring deep within the Andromeda galaxy. When combined with a previously observed outer ring, the presence of both dust rings suggests a long-ago disturbance whose effects are still expanding outward through Andromeda.