Star with a carbon atmosphere - November 22, 2007
Star light, star bright, first star… with a pure carbon atmosphere was reported in Nature last night.
Actually the researchers report finding 8 weird stars in data from the Sloan Digital Sky Survey, whose characteristics can be explained by a model of a star with a pure carbon atmosphere.
As stars’ helium burns off, leaving behind ashes of carbon and oxygen, they usually turn to white dwarfs: a core of carbon and oxygen surrounded by an atmosphere of hydrogen or helium. But these big boys seem to be bare dwarf cores, with no helium or hydrogen in the atmosphere – just carbon (press release). No one knows why. One theory is that the stars have evolved from those not quite massive enough to explode as supernovae.
The discovery was made by researchers who were frantically trying to explain the weird data coming from some particularly hot white dwarfs. "Out of pure desperation, I decided to try modeling a pure-carbon atmosphere. It worked," says Patrick Dufour of the University of Arizona, Tucson (press release).
"It will be a challenge to try to explain how they form and what does this tell us about stellar evolution," Dufour told Reuters.
There are plenty of weird star types out there, including ‘runaway’ stars that have abnormally high speeds relative to the stuff around them, really big stars that are rapidly blowing apart, and ‘carbon stars’, which have more carbon than oxygen and so take have a sooty atmosphere and a red appearance.
Such a discovery happens about ‘once a decade’ according to an expert quoted in Science’s coverage of the story.
Artists' concept of the surface of a carbon-atmosphere white dwarf star. Credit: M.S. Sliwinski and L. I. Slivinska of Lunarismaar