How massive can a white dwarf be if it spins once every 29.6 seconds?

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CTCV J2056–3014 is a nearby cataclysmic variable about 853 light-years from Earth, with an orbital period of approximately 1.76 hours. Its recently reported X-ray properties suggest that it is an unusual accretion-powered intermediate polar containing a white dwarf that spins once every 29.6 seconds.

Its low X-ray luminosity and relatively modest accretion rate per unit area suggest that the shock does not occur near the white dwarf’s surface. It has been argued that, under these conditions, the shock’s maximum temperature cannot be used directly to determine the white dwarf’s mass. The mass inferred under the assumptions discussed would be around 0.46 solar masses.

This theoretical study explored the rapidly rotating white dwarf’s stability using a modern equation of state (EoS) that includes electron–ion, electron–electron, and ion–ion interactions. Using this EoS, the researchers determined the mass-density thresholds at which pycnonuclear fusion reactions begin. They examined how microscopic stability and rapid rotation affect the structure and stability of white dwarfs with helium, carbon, oxygen, and neon compositions.

The analysis yielded a minimum mass of 0.56 solar masses and a maximum mass of around 1.38 solar masses for the white dwarf in CTCV J2056–3014. If its mass is close to the lower limit, rapid rotation would give it an equatorial radius on the order of 10⁴ km. This is significantly larger than the radius of a nonrotating white dwarf of average mass, 0.6 solar masses, whose radius is on the order of 7 × 10³ km.

Changes in the temperature and composition of the stellar matter were found to have negligibly small effects on J2056–3014’s minimum mass.