In roughly 3 billion years, before our Sun expands into a red giant, a collision of titans will occur. Our Milky Way Galaxy will smash into its nearest large neighbor, Andromeda (also known as M31). As the galaxies approach each other, strong tidal forces will seriously deform their stately spiral structures, sending stars careening in all directions as their galactic orbits are perturbed. Even though these galaxies contain hundreds of billions of stars, individual stars will not collide because they are very small relative to the separation between them. But interstellar gas clouds will collide and collapse, triggering furious starbirth in both galaxies. Eventually, the two vast congregations will merge to form a giant elliptical galaxy.

While none of us will be around to witness these cataclysmic events, astronomers can simulate them on supercomputers, and compare the results to observations of actual merging galaxies. Astrophysicist John Dubinski has been simulating galaxy collisions for a decade. This Web page allows you to view some of his most recent animations of the Milky Way–Andromeda collision. To see more animations of galaxy collisions, visit his Dubinski's Web site. You can also order his recently released DVD Gravitas,, which includes some of his animations set to the music of Toronto-based composer John Kameel Farah.

Click on the images below to view some of these simulations.

In this speculative simulation, the Milky Way and Andromeda galaxies initially pass by each other at a range of 60,000 light-years without colliding. But complex gravitational interactions distort the shape of each galaxy, generating tidal tails and bridges. The close passage dissipates orbital energy, so the stellar cities collide on a second pass, finally merging after several convulsions. The last remnants of the smashed spirals show up as shells and ripples surrounding a newborn elliptical galaxy. To view this .mov file, first download Apple's free QuickTime player. File size: 19.6 MB. John Dubinski