Busted! Astronomers Nab Culprit in Galactic Hit-and-Run

Astronomers have new evidence that the Andromeda spiral galaxy was involved in a violent head-on collision with the neighboring dwarf galaxy Messier 32 (M32) more than 200 million years ago. This infrared photograph taken with NASA's Spitzer Space Telescope revealed a never-before-seen dust ring deep within the Andromeda galaxy (highlighted by the inset). When combined with a previously observed outer ring, the presence of both dust rings suggests that M32 plunged through the disk of Andromeda along Andromeda's polar axis approximately 210 million years ago. Credit: NASA/JPL/P. Barmby (CfA)