A massive
explosion in the deep reaches of space stemmed not from one dying star, as is
typical, but from two dead ones that collided as the climax of a long orbital
dance, new research shows.
Two white
dwarf stars slowly spiraled into each other to touch off a supernova
explosion called SN 2006gz and discovered last year in a spiral galaxy some
300 million light-years from Earth, said the study's lead author Malcolm
Hicken.
"This
finding shows that nature maybe richer than we suspected, with more than one
way to make a white dwarf explode," said Hicken, a graduate student at the
Harvard-Smithsonian Center for Astrophysics.
The
research is detailed in the Nov. 1 issue of the Astrophysical Journal Letters.
A white
dwarf is the remains of a star with too little mass on its own to end its
stellar life as a supernova, the cataclysmic explosions that redistribute material
back into space. The Sun, as well as stars with up to eight times its mass,
will ultimately end up as white dwarfs.
Astronomers
split supernovas
into two categories: the explosion of a young, massive star whose core
collapses, or the cataclysmic result of a white dwarf star siphoning gas from a
stellar companion until it, too, blows itself apart.
Originally,
astronomers thought that supernova SN 2006gz was just another example of a
white dwarf stealing material from a partner star. But a closer look revealed
signs of extra carbon and silicon, hallmarks of a smash-up between two white
dwarf stars.
SN 2006gz
was also brighter than researchers expected, suggesting that its origins
included more material than the 1.4 solar mass upper limit of a single white
dwarf star.
The
observations offer new evidence for what until now has been only a theoretical
way for supernovas to form. Since single white dwarf-spawned supernovas, also
known as Type 1a explosions, are used as a standard
for judging cosmic distances, separating them from those caused by two-white
dwarf collisions will be critical for future research, Hicken said.
"[W]e
have to be careful not to mistake a double white-dwarf explosion for a single
white-dwarf blast," he added. "SN 2006gz was easy to recognize, but
there may be less clear-cut cases."
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