Supernova hits star, reveals its origin

New York: A team of astronomers have witnessed a supernova smashing into a nearby star, shocking it and creating an ultraviolet glow that reveals the size of the companion. In a type Ia supernova, a white dwarf star explodes after it gains matter from a companion star in the same binary star system. One of the leading theories is that the supernova happens when two white dwarf stars merge.

But a competing theory says that the companion could be a normal or giant star that survives the explosion, although not without some damage. The supernova is expected to hit the companion star, creating a shock wave that glows in ultraviolet light. The origin of type Ia supernovae, the standard candles used to reveal the presence of dark energy in the universe, is one of astronomy's most beguiling mysteries.

Astronomers know they occur when a white dwarf explodes in a binary system with another star, but the properties of that second star -- and how it triggers the explosion -- have remained elusive for decades. The better we understand the origin of type Ia supernovae, the better we can use them as standard candles for cosmology.