Galaxy Collisions and Mergers Modern research into galaxy formation is also exploring the role that mergers and collisions of galaxies plays in the structure of galaxies. The distances between galaxies is large, but compared to the size of the galaxies, the distances are not extremely large. Stars inside a galaxy do not collide because the distances between them are hundreds of thousands to millions of times larger than the sizes of the stars. The distances between galaxies are only a few tens of times bigger than the galaxy sizes. Our Milky Way has several small galaxies orbiting it that are one to two Milky Way diameters away. The closest large galaxy, the Andromeda Galaxy, is only about 30 Milky Way diameters away. Galaxies in rich clusters are closer to each other than that. Collisions take place over very long timescales compared to the length of our lifetime---several tens of millions of years. In order to study the collisions, astronomers use powerful computers to simulate the gravitational interactions between galaxies. The computer can run through a
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