A long time ago (at least a billion years) two galaxies far far away (17.3 million light years) ran into each other dead center to merge into what we see today, the Black Eye Galaxy (M64). Their merger caused a rather unique feature among spiral shaped galaxies. M64 can be defined as a galaxy within a galaxy.
I've increased the contrast of colors to bring out this feature. The inner blue-tinted region rotates in one direction while the outer red-tinted region rotates in the opposite direction. This, as well as the merger itself, has created a sort of "backwater" of dust that resembles a black eye.