Dust Strangely Vaporized by Stellar Explosion

Artist concept of the RS Ophiuchi binary system shortly after a white dwarf (right) has exploded as a nova. Scientists have detected dust in the system, depicted here as spiral dust lanes. CREDIT: Casey Reed

Explosions of small stars, long thought to create stellar dust, actually sweep dust away, scientists discovered.

For years, researchers have observed swirling dust clouds around systems called recurring novas, which periodically explode. New images of a distant nova have now overturned astronomers' long-standing assumption that the dust originates in the blasts.

Scientists recently observed the RS Ophiuchi system, where a small white dwarf star and large red giant orbit each other. Over time, the giant sheds its outer layer of gas, which the dwarf sweeps up. The little star's mass grows gradually, eventually reaching a tipping point, when the top layer ignites in a thermonuclear explosion and expels the surface into space. The process then starts over — astronomers have already seen this system "go nova" in 1898, 1933, 1958, 1967 and 1985.

When RS Ophiuchi blew again in February 2006, researchers took advantage of a new instrument, called the Keck Nuller, at the W. M. Keck Observatory in Mauna Kea, Hawaii, to watch the event in action. The Nuller used two giant telescopes to block out the overwhelming light from the explosion so scientists could study its fainter surroundings.

They were surprised to see no dust in the bright zone around the star and only to see dust farther away, where the blast wave had not yet reached. The researchers surmised that the detonation had vaporized nearby dust particles, and that the outer dust must have been created before the bang.

"This flies in the face of what we expected," said Richard Barry, an astronomer at NASA's Goddard Space Flight Center in Greenbelt, Md., who headed up the observations. "Astronomers had previously thought that nova explosions actually create dust."

The team suspects the dust is really produced when the white dwarf plows through the red giant's trail of debris, creating patches of gas where atoms are cool and dense enough to clump together into dust particles.

The findings will be detailed in the May 1 issue of the Astrophysical Journal.

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