John Dubinski (University of Toronto)

We live in the Milky Way Galaxy, a collection of gas, dust, and hundreds of billions of stars. About two million light years (20 billion billion kilometers) away lies the Andromeda Galaxy, a spiral galaxy similar in size and shape to our Milky Way. Current measurements suggest that, in about three billion years, the Milky Way and Andromeda galaxies may collide. What will happen? The stars in the galaxies, our Sun included, will probably not hit each other, but the galaxies' mutual gravity will probably pull, twist, and distort them until, about a billion years later, a new elliptical-shaped galaxy is born.

Gravity and tides at work

This movie shows a supercomputer simulation of one possible collision scenario between the Milky Way and Andromeda. Each spiral galaxy is represented by a disk of stars surrounded by a spherical dark matter halo. The simulation contains over 100,000,000 virtual particles. The Milky Way is shown face-on and is initially at the bottom of the frame while Andromeda moves from the top of the frame down and is tilted from this perspective. The movie's field of view is about one million light years (10 billion billion kilometers) across, and the total elapsed time of the movie is about 1 billion years. The complex patterns and structures created during the collisions are caused by tides, the same process that works on Earth's oceans. The gravitational pull of the each galaxy's stars and dark matter twist, tear, and distort their original disk-like structures, leaving a single elliptical galaxy and lots of tidal debris after all is said and done.

Gordon Myers