Supersoft X-ray source found in helium-burning white dwarf binary

Astronomers have discovered a binary star system in which a white dwarf is accreting helium from its companion, leading to stable helium burning on its surface. The system was identified due to bright super-soft X-rays originating from the nuclear fusion of the overflowed gas near the surface of the white dwarf. The measured luminosity suggests that the mass of the white dwarf is growing more slowly than previously thought possible, which may help to understand the number of supernovae caused by exploding white dwarfs. The discovery could help to further constrain the conditions for Type Ia supernova progenitors.