Like a celestial exhibitionist, a star in the constellation Draco the Dragon has thrown off its mantle to expose its bare core, and it has taken astronomers aback. The surface of the star, H1504+65, is a sizzling 200,000 kelvin, making it the hottest white dwarf star ever recorded, recent NASA satellite data reveal. What's more, the stellar core is almost entirely carbon and oxygen, with no trace of hydrogen and helium--the main constituents of stars. H1504+65 is the first star identified that lacks helium altogether.
White dwarfs are the slowly cooling cores of sunlike stars in which nuclear fusion has stopped. Given its high temperature, H1504+65 must have shut down its fusion reactions very recently--maybe just a couple of centuries ago, according to Klaus Werner of the University of Tübingen in Germany. Werner led the team that studied the star with the Far Ultraviolet Spectroscopic Explorer and the Chandra X-ray Observatory.
But the team, which describes its findings in the July issue of Astronomy & Astrophysics, can't explain all the star's oddities, especially its absence of helium. Maybe the star's helium atmosphere has been blown away by a sudden thermonuclear ignition of carbon, says Werner. If so, future observations should reveal the telltale presence of sodium, one of the products of this reaction.
