White dwarf "sibling rivalry" explodes

Astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) have found that a supernova discovered last year was caused by two colliding white dwarf stars. The white dwarfs were siblings orbiting each other. They slowly spiraled inward until they merged, touching off a titanic explosion. CfA observations show the strongest evidence yet of what was, until now, a purely theoretical mechanism for creating a supernova.