Numerical models for stationary superfluid neutron stars in general relativity with realistic equations of state

Abstract

We present a numerical model for uniformly rotating superfluid neutron stars, for the first time with realistic microphysics including entrainment, in a fully general relativistic framework. We compute stationary and axisymmetric configurations of neutron stars composed of two fluids, namely superfluid neutrons and charged particles (protons and electrons), rotating with different rates around a common axis. Both fluids are coupled by entrainment, a non-dissipative interaction which in case of a non-vanishing relative velocity between the fluids, causes the fluid momenta being not aligned with the respective fluid velocities. We extend the formalism by Comer and Joynt [1] in order to calculate the equation of state (EoS) and entrainment parameters for an arbitrary relative velocity as far as superfluidity is maintained. The resulting entrainment matrix fulfills all necessary sum rules and in the limit of small relative velocity our results agree with Fermi liquid theory ones, derived to lowest order in the velocity. This formalism is applied to two new nuclear equations of state which are implemented in the numerical model. We are able to obtain precise equilibrium configurations. Resulting density profiles and moments of inertia are discussed employing both EoSs, showing the impact of entrainment and the dependence on the EoS.

Vortex pinning in the superfluid core of neutron stars and the rise of pulsar glitches

“…as shown in an accompanying paper (Sourie & Chamel 2020). The neutron Magnus force arising from the relative flow of superfluid neutrons with velocity v i nv i L is given by…”

Force on a neutron quantized vortex pinned to proton fluxoids in the superfluid core of cold neutron stars

“…5 As shown in the accompanying Letter (Sourie & Chamel 2020), the coefficient B (B ) is associated with the dissipative (conservative) contribution in the smooth-averaged mutual-friction force arising at scales large compared to the intervortex spacing.…”

“…The general expression of the vortex velocity is calculated and the role of pinning on the vortex dynamics is discussed. The implications for pulsar glitches are studied in an accompanying paper (Sourie & Chamel 2020).…”

Thermodynamics of uncharged relativistic multifluids

“…Since multifluid models in General Relativity must be considered for an accurate modelling of superlfuid neutron star interiors, the problem of how to embed the information given by a microphysical equation of state within a covariant phenomenological model is of primary importance: the wide range of applications spans from equilibrium models of stellar structure (e.g. Andersson & Comer 2001;Sourie et al 2016), to the study of stellar oscillations (e.g. Andersson et al 2002;Gusakov & Andersson 2006), pulsar glitches in General Relativity (e.g.…”