Milky Way and Andromeda Collision

It is currently believed that in about 5 billion years, our galaxy, the Milky Way, and the nearby Andromeda Galaxy (M31), will collide. While individual stars in the galaxies are unlikely to collide, the powerful gravitational interaction between the two galaxies will tear the two spiral galaxies apart, ultimately forming a new elliptical galaxy. Great simulations of this event, done by John Dubinski at the University of Toronto using supercomputers and including 100,000,000 particles, can be found here. (Save the mpg files to disk and play them manually in order to increase the size.)