Supernovae and Supernova Remnants
A supernova is a stellar explosion that may occur in some stars more massive than the Sun when they reach a point late in their evolution. Such explosions are extremely bright and can outshine an entire galaxy for a short period of time. During a supernova explosion, most of a star's outer layers are expelled at high velocity (30,000 km/s) into interstellar space. The resulting shock wave in a shell of expanding gas and dust is known as a supernova remnant.
The 18th-century French astronomer Charles Messier recorded 1 supernova remnant in his Messier Catalog of deep sky objects. See Wikipedia for an excellent article about supernovae and supernova remnants.
Click on each thumbnail to see a larger image.