Interacting galaxies

Galaxies are grand yet fragile structures. When they pass close to each other or collide, their mutual gravity pulls them apart, twisting and distorting their shapes. Usually, two galaxies that collide will eventually merge to become one. Such mergers appear to be a standard feature in galaxy formation. During galaxy encounters, it is not the stars within the galaxies, but rather their gas clouds that collide.

This silent time-lapse movie, produced with the help of supercomputers, shows what can happen when two large spiral galaxies collide — a billion years of cosmic history compressed into a few seconds.

Computer simulations are the laboratory in which astronomers study galaxy interactions. Because an actual encounter takes billions of years, observations provide just one snapshot of an interaction. Computer simulations can follow the entire development of an encounter, and explore variations. Many observed galaxy interactions have been re-created on the computer, providing insights into the structure of the galaxies and stages and timing of the encounter, and the possible end results.