Quasiequilibrium sequences of synchronized and irrotational binary neutron stars in general relativity. II. Newtonian limits

TL;DR

This paper investigates Newtonian equilibrium sequences of binary neutron stars with polytropic equations of state, revealing conditions for stability and termination points in synchronized and irrotational systems.

Contribution

It introduces an improved spectral method for accurate computation of binary systems with stiff equations of state and analyzes the stability and termination points of these systems.

Findings

Turning points of total energy appear only for certain adiabatic indices.

Synchronized binaries terminate by contact between stars.

Irrotational binaries terminate at a mass shedding limit.

Abstract

We study equilibrium sequences of close binary systems composed of identical polytropic stars in Newtonian gravity. The solving method is a multi-domain spectral method which we have recently developed. An improvement is introduced here for accurate computations of binary systems with stiff equation of state ($\gamma > 2$). The computations are performed for both cases of synchronized and irrotational binary systems with adiabatic indices $\gamma=3,~2.5,~2.25,~2$ and 1.8. It is found that the turning points of total energy along a constant-mass sequence appear only for $\gamma \ge 1.8$ for synchronized binary systems and $\gamma \ge 2.3$ for irrotational ones. In the synchronized case, the equilibrium sequences terminate by the contact between the two stars. On the other hand, for irrotational binaries, it is found that the sequences terminate at a mass shedding limit which corresponds to a detached configuration.