Viscosity of neutron stars has been a continuing area of research for many years now. Recently interest in this field has revived because of the possibility of URCA processes in neutron stars. In this paper we report calculation of the bulk viscosity of neutron stars from these processes. For this purpose we have used theβ-decay rates which were calculated without making the usual approximations of neglecting the neutrino momentum and using the nuclear mean field theory for the description of interacting nuclear matter. Also we have not restricted our calculation to the linear regime which corresponds to the assumption that fluctuations in the chemical potential away fromβ-equilibrium remain small: Δμ/kT ≪ 1. We find that for large amplitude fluctuations, where the linear approximation is not valid, bulk viscosity increases by many orders of magnitude. Also, as against strange matter stars, where the viscosity first increases with increasing temperature and then starts decreasing beyond 0.1 MeV, we find that the viscosity increases uniformly with temperature at least up to 2MeV. We discuss the implications of these results for the stability of neutron stars.
Volume 94, 2019
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