One glance at this picture lets you know why M51 is commonly called The Whirlpool. At 23 million light years away, it's visible through binoculars (barely; I always have a hard time spotting it), so when you point something like Hubble at it you know you'll be getting an incredible view
This gorgeous shot is actually a composite of four different filtered images by Robert Gendler, an accomplished astrophotographer. The original release, done in 2005, was of course beautiful, but Robert took a stab at it and was able to make it even better.
The Whirlpool is actually two galaxies interacting with one another. The spiral galaxy is nearly face-on, and you can easily trace the magnificent arms, laced with red gas clouds forming new stars, and dark lanes of dust created when stars are born and when they die. The other galaxy is the orange blobby one, a dwarf irregular. It may have already passed through the bigger galaxy twice, and will eventually merge with it. We think all big galaxies grow by consuming smaller ones in this manner. In a few hundred million more years there won't be two galaxies left to see, just one somewhat bigger one. Our own Milky Way Galaxy probably underwent a similar event many times!Get the high-res version here. Image Credit: NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI). Additional Processing: Robert Gendler