On general relativistic uniformly rotating white dwarfs

Details On general relativistic uniformly rotating white dwarfs On general relativistic uniformly rotating white dwarfs

2012-04-10

arxiv.org/abs/1204.2070v1

Astronomy and Astrophysics

Astrophysics

Solar and Stellar Astrophysics

Submitted to The Astrophysical Journal

Scientific paper

Uniformly rotating white dwarfs (RWDs) are analyzed within the framework of general relativity. The Hartle's formalism is applied to construct self-consistently the internal and external solutions to the Einstein equations. The relativistic Feynman-Metropolis-Teller EoS that generalizes the Salpeter's one taking fully into account the finite size of nuclei, the Coulomb interactions as well as electroweak equilibrium in a self-consistent relativistic fashion is used to describe the WD matter. The mass, radius, angular momentum, eccentricity and quadrupole moment of RWDs are calculated as a function of the central density and rotation angular velocity. We construct the region of stability of RWDs taking into account the mass-shedding limit, inverse beta-decay instability, and the boundary established by the turning points of constant angular momentum sequences that separates stable from secularly unstable configurations. We found the minimum rotation periods 0.3, 0.5, 0.7 and 2.2 seconds and maximum masses 1.500, 1.474, 1.467, 1.202 solar masses for He, C, O, and Fe WDs, respectively. The existence of stable WDs with rotation periods as short as the aforementioned ones can naturally explain, within the model based on massive and fast rotating WDs, the range of rotation periods 2-12 seconds observed in SGRs and AXPs. By using the turning-point method we found that, in contrast with the current literature, RWDs can indeed reach the onset of secular instability and we give the range of WD parameters where it occurs. We also construct constant rest-mass evolution tracks of RWDs at fixed chemical composition and show that, by loosing angular momentum, Sub-Chandrasekhar RWDs can experience both spin-up and spin-down epochs depending on their initial mass and rotation period. On the contrary, super-Chandrasekhar RWDs can only spin-up by angular momentum loss.

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