Dusty spirals spun = by incognito stars - space - 17 August 2006

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17 August 2006

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Dusty spirals spun by incognito stars

21:25 17 August 2006=20
NewScientist.com news service=20
Hazel Muir

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Each of the five bright red "stars" (labelled) in = the=20 Quintuplet cluster is thought to be a double star system boasting a = pinwheel=20 nebula (Image: P Tuthill/D Figer/Sydney U/Keck Obs/NASA/RIT)

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Five enigmatic stars in a cluster at the heart of the Milky Way have = each=20 turned out to be mammoth young double star systems, trailing dust into = elegant=20 pinwheel shapes as they live fast and die young.

The Quintuplet, discovered in 1990, is a cluster of hundreds of stars = around=20 26,000 light years away, near our Galaxy=92s centre. It takes its name = from five=20 prominent red stars cocooned in dust, which have puzzled = astronomers.

Starlight normally has sharp lumps and bumps at different wavelengths = that=20 characterise a star=92s composition, age and size. But the five = Quintuplet stars=20 emit curiously uniform, featureless light across a wide waveband.

=93When we use our regular barrage of observations that we throw at = most stars,=20 we come up with no answers,=94 says Donald Figer from the Rochester = Institute of=20 Technology in New York state, US.

Now Figer his colleagues, led by Peter Tuthill from the University of = Sydney=20 in Australia, have revealed that all we=92re seeing is the dust around = five double=20 star systems, which produces the illusion of five single stars.

Violent wind

They used one of the twin 10-metre Keck telescopes on Mauna Kea, = Hawaii, to=20 create infrared images of the five Quintuplet stars in unprecedented = detail. At=20 least two revealed dust lanes in a clear spiral shape.

Figer believes the spirals are created by pairs of stars, each = containing a=20 so-called =93Wolf-Rayet star=94 with a violent wind blowing outwards at = about 2000=20 kilometres per second. Such stars represent a short-lived stage in the = lives of=20 stars born with the mass of at least 25 Suns.

The fast wind of the Wolf-Rayet star crashes into that of the stellar = giant=20 orbiting around it. Dense, cool dust forms in the region where the two = winds=20 collide, and this carves out a spiral as the two stars circle each = other. =93You=20 have an effect like a garden hose being twirled around,=94 Figer told = New=20 Scientist.

If the stars in the Quintuplet are indeed Wolf-Rayet types, the = finding=20 should shed light on this fleeting life-stage =96 the stars will soon = blow=20 themselves to smithereens.

=93It=92s the last stage before they go supernova, probably within a = few hundred=20 thousand years,=94 says Figer.

Journal reference: Science (vol 313, p 935)

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