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Asteroids might spark supernovas: rocky debris falling into white dwarfs may trigger explosions.

A few well-aimed asteroids might be all it takes to make a star explode.

Rocky debris in the atmosphere of a white dwarf, the core of a long dead star, could trigger an explosion known as a type la supernova. The proposal, reported online February 1 at arXiv.org, suggests a new way to create this type of supernova, whose origins are debated.

While the mechanism that might destroy the white dwarf isnt clear, "the idea isnt pure speculation," says lead author Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics. The atmospheres of many of these stars are laced with elements such as carbon and silicon that should have sunk deep into the star. Since researchers can see these atoms, there must be a steady supply of material, most likely from asteroids that wander too close.

Most asteroids will be torn apart by a white dwarfs gravity. But Di Stefano and colleagues suggest that occasionally a few intact asteroids, or even a small planet, might hit a white dwarf directly. The influx of material might trigger thermonuclear fusion in the stars atmosphere that sends a shock wave through the star.

White dwarfs explode when their mass exceeds a threshold called the Chandrasekhar limit, about 1.4 times the mass of the sun. Astronomers debate how white dwarfs surpass that limit. A white dwarf might steal gas from a partner star. Or two white dwarfs orbiting each other might collide and destroy themselves. But scientists cant find companion stars in preexplosion images. And there don't seem to be enough binary white dwarfs with the mass to trigger a supernova.

An asteroid falling into a white dwarf might provide enough mass to push a star over the Chandrasekhar limit. Or more likely, Di Stefano says, an asteroid might trigger a thermonuclear explosion in the helium enveloping a lower-mass white dwarf that is well below the limit.

"Its interesting speculation thats not yet substantiated," says astrophysicist Adam Burrows of Princeton University.

Di Stefano acknowledges there are lots of unknowns. Future telescopes might detect flares from impacts, which could give scientists a better handle on what types of objects, if any, hit white dwarfs before being torn apart.

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Title Annotation:ATOM & COSMOS
Author:Crockett, Christopher
Publication:Science News
Date:Mar 7, 2015
Words:365
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