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. In the conventional picture for the type of supernova discovered last year — Supernova 2006gz — a white dwarf star collects gas from a companion star until it undergoes catastrophic nuclear fusion and blasts itself apart. (A white dwarf star is a small, extremely dense star at the end of its life.) But in this case, the evidence showed that the supernova was the result of the collision of two white dwarf stars, a phenomenon known previously only in theory. In addition to providing the first example of a new way to make supernovae, SN 2006gz holds implications for the field of cosmology.

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