Stephan's Quintet
This grouping of five galaxies 280 million light-years away in the constellation Pegasus is known as Stephan's Quintet. Four of the five galaxies are experiencing a violent merger, where they crash into one another an eventually form one galaxy. Though it looks like the central blue galaxy is part of this clan, this is an illusion. It is actually a foreground galaxy only about 40 million light-years away.
This image, from the Arizona Sky Center, required a 5-hour exposure using the 32-inch Schulman telescope.
Image: Adam Block and Vic Eden/Mount Lemmon SkyCenter/University of Arizona [high-resolution]
Caption: Wired Science