Equilibrium configurations of relativistic White Dwarfs

The Feynman-Metropolis-Teller treatment for compressed atoms is here reconsidered in the framework of the relativistic generalised Fermi-Thomas model, obtained by Ruffini et al. Physical properties of a zero temperature plasma is thus investigated and the resulting equation of state, which keeps into account quantum, relativistic and electromagnetic effects, is applied to the study of equilibrium configurations of relativistic White Dwarfs. It is shown that numerical evaluation of such configuration leads, for the same central density $\rho_c$, to smaller values of radius R and of mass M than in the classical works of Chandrasekhar and Salpeter, the deviations being most marked at the lowest densities (up to 30% from the Chandrasekhar model and 10% from the Salpeter one for $\rho_c \sim 10^6g/cm^3$, corresponding to $M \sim 0.2 M_{\odot}$). At high densities we considered the occurrence of inverse beta decays, whose effect is to introduce gravitational instability of the configurations. We consequently find the maximum mass of White Dwarfs, which, for an Oxygen and an Iron WD, is respectively $1.365 M_{\odot}$ and $1.063 M_{\odot}$.