Galaxies in Collision

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.

Spiral Metamorphosis
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
Future Sky
This movie shows how the night sky will appear over the next 4 billion years as the Andromeda Galaxy approaches and eventually mergers with our galaxy. The arch of the Milky Way is apparent at first as a band of stars, and faraway Andromeda is seen scrolling past beneath the arch but slowly growing in size as it approaches. When the two galaxies intersect, the Sun is flung out far from the colliding pair of galaxies and our view oscillates between a remote view of events to a wild ride right through the center of the galactic bulge. The Sun’s orbit is no longer circular but now follows a convoluted pattern with the distorted gravitational field of the merging galaxies. A final look back from the far-flung Sun shows the final merger of the two galaxies. To view this .mov file, first download Apple's free QuickTime player. File size: 27.9 MB.
John Dubinski
3D Metamorphosis
This animation shows the merger in three dimensions. To view this movie, don 3-D anaglyph glasses. To view this .mov file, first download Apple's free QuickTime player. File size: 21.4 MB.
John Dubinski
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