Although it doesn't have the same name recognition as Andromeda, the Whirlpool Galaxy or the Sombrero Galaxy, NGC 3521 (pictured above and below) is easily one of most stunning galaxies I've come across.
Found about 40 million light-years from Earth toward the constellation of Leo, NGC 3521 has a somewhat obvious nickname: the Bubble Galaxy. When viewed from afar, it appears to be completely encased in a large, but faint, bubble. What looks like a second bubble also surrounds its nucleus.
A new image zeroes in on a small sliver of that particular section. From this vantage point, we can see the key features that give NGC 3521 its flocculent spiral designation.
From the European Southern Observatory:
Zooming back outward, to the bubble itself, astronomers believe the shell is an artifact of galaxy mergers.. namely when NGC 3521 and several smaller galaxies collided. In the immediate aftermath, a bunch of gas, dust and rogue stars were strewn all throughout space—eventually coalescing back into a familiar form (features such as halos, stellar streams and tidal tails are common in events like this).
The merger also led to the formation of many star clusters, which are pink-tinged. Those with a blue-white hue are high-mass, bright and incredibly hot. They will only live for a few hundred million years before they explode as supernovae—reseeding space with raw materials for star-formation. (See a larger image here)