Every so often, one of the galaxies drifting through the universe will collide with another, creating the kind of spectacle seen here. This pair of crashing galaxies is called "The Antennae" because of the long streamers of stars thrown off early in the collision.

Collisions like these last hundreds of millions of years and were probably much more common in the early universe, when galaxies were much closer together.

GALACTIC CRASH SCENE: RECONSTRUCTING COSMIC COLLISIONS

When confronted with the spectacular messes seen in this Hubble picture, astronomers usually resort to computer models of galaxy collisions. These models use known laws of physics to simulate what will happen when two galaxies collide. The trick is to specify the properties of the inital galaxies — size, shape, direction of motion, and speed — so that when they collide, they produce something similar to the observed mess.