Merging galaxies play a large role in the evolution of galaxies and the formation of elliptical galaxies in particular. However there are only a few merging systems close enough to be observed in depth. NGC 3921, found in the constellation of Ursa Major (The Great Bear), is an interacting pair of disc galaxies in the late stages of its merger. Observations show that both of the galaxies involved were about the same mass and collided about 700 million years ago. You can see clearly in this Hubble Space Telescope image the disturbed morphology, tails and loops characteristic of a post-merger.