Dufour studied a special class of white dwarfs with an atmosphere of helium and carbon during his dissertation. He found that the spectrum of some of them, with relatively warm surface temperatures, could only be explained by an atmosphere of pure carbon. "Nobody believed that such stars exist, " says Dufour, "we were excited and excited."
The researchers assume that the carbon dwarfs arise from particularly heavy precursor stars, with a mass of nine to eleven times the mass of the sun. That's about the limit at which a star is heavy enough to explode as a supernova. The researchers around Dufour have already found a model star that could be an earlier stage of development on the way to the carbon dwarf: The object H1504 + 65 is the hottest white dwarf known so far. Astronomers assume that it consists only of oxygen and carbon. "We think this star could get a carbon atmosphere when it cools, " says Dufour. The researchers want to take a closer look at their eight carbon dwarfs in December with the MMT Observatory on Mount Hopkins to determine their mass. With the help of these data, they hope to delimit the hitherto inaccurately known mass limit, at which a star becomes a supernova.Patrick Dufour (University of Arizona, Tucson) et al .: Nature, vol. 450, p. 522 Ute Kehse advertisement