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.
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.