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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