Antennae Galaxies (NGC 4038 & NGC 4039)
The Antennae Galaxy is actually a pair of galaxies that appear to be merging in a giant cosmic collision. During the lengthy course of the collision billions of new stars will be formed.
Colliding galaxies are not particularly rare, but the Antennae Galaxies are among the nearest examples of such collisions. The orange areas to the left and right of image centre are the cores of the the original galaxies.