Andromeda Galaxy, M31, is a large spiral galaxy located about 2.5 million light years away. It is the closest major galaxy to our own Milky Way. Andromeda is larger than the Milky Way and contains more stars. Still, the Milky Way contains more mass due to what may be a larger amount of dark matter. There is evidence that Andromeda may have collided with another galaxy, M32, more than 200 million years ago, and it is expected that it will collide with the Milky Way in several billion years.