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Dead Stars Collide, Explode

Dead Stars Collide, Explode
This artist's conception shows two white dwarf stars spiraling in toward each other until they collide. A collision like this is believed to have spawned supernova 2006gz.
(Image: © NASA/Dana Berry, Sky Works Digital.)

A massiveexplosion in the deep reaches of space stemmed not from one dying star, as istypical, but from two dead ones that collided as the climax of a long orbitaldance, new research shows.

Two whitedwarf stars slowly spiraled into each other to touch off a supernovaexplosion called SN 2006gz and discovered last year in a spiral galaxy some300 million light-years from Earth, said the study's lead author MalcolmHicken.

"Thisfinding shows that nature maybe richer than we suspected, with more than oneway to make a white dwarf explode," said Hicken, a graduate student at theHarvard-Smithsonian Center for Astrophysics.

Theresearch is detailed in the Nov. 1 issue of the Astrophysical Journal Letters.

A whitedwarf is the remains of a star with too little mass on its own to end itsstellar life as a supernova, the cataclysmic explosions that redistribute materialback into space. The Sun, as well as stars with up to eight times its mass,will ultimately end up as white dwarfs.

Astronomerssplit supernovasinto two categories: the explosion of a young, massive star whose corecollapses, or the cataclysmic result of a white dwarf star siphoning gas from astellar companion until it, too, blows itself apart.

Originally,astronomers thought that supernova SN 2006gz was just another example of awhite dwarf stealing material from a partner star. But a closer look revealedsigns of extra carbon and silicon, hallmarks of a smash-up between two whitedwarf stars.

SN 2006gzwas also brighter than researchers expected, suggesting that its originsincluded more material than the 1.4 solar mass upper limit of a single whitedwarf star.

Theobservations offer new evidence for what until now has been only a theoreticalway for supernovas to form. Since single white dwarf-spawned supernovas, alsoknown as Type 1a explosions, are used as a standardfor judging cosmic distances, separating them from those caused by two-whitedwarf collisions will be critical for future research, Hicken said.

"[W]ehave to be careful not to mistake a double white-dwarf explosion for a singlewhite-dwarf blast," he added. "SN 2006gz was easy to recognize, butthere may be less clear-cut cases."

 

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