Multiple Blasts 
A white dwarf would seem to be one of the most innocuous objects in the universe. It’s the small dead core of a once-normal star like the Sun. It no longer produces energy through nuclear reactions, but it continues to shine because it’s extremely hot.
But give a white dwarf a companion star and things change in a hurry. Interactions between the two can trigger explosions — big ones that blast away the white dwarf’s outer layers, or gigantic ones that blast the entire star to cosmic dust. And sometimes, a single white dwarf can do both.
A research team led by Ben Dilday of UC-Santa Barbara found evidence of a double-blaster in a galaxy 600 million light-years away. A supernova flared to life there, briefly outshining its entire home galaxy. The supernova was the complete destruction of a white dwarf.
But observations revealed expanding shells of gas and dust around the supernova. The shells were produced by earlier nova explosions.
The two types of explosions are related. Both occur when gas piles up on the surface of a white dwarf. A nova is an explosion of the shell of extra gas, while a supernova is the disruption of the entire star.
To complicate matters even more, that’s only one of the ways in which a white dwarf can become a supernova. The other is when two white dwarfs ram together. Astronomers have seen evidence of a few of these collision-powered supernovae — the violent ends of otherwise quiet stars.
Script by Damond Benningfield, Copyright 2012