Various features of quasiequilibrium sequences of binary neutron stars in general relativity

TL;DR

This paper presents numerical calculations of quasiequilibrium sequences of binary neutron stars in general relativity, analyzing different spin states and equations of state to understand their stability and orbital characteristics.

Contribution

It provides new numerical results for binary neutron star sequences in the IWM approximation, including both synchronized and irrotational spins, and proposes a conjecture relating Newtonian and relativistic stability indicators.

Findings

Identification of the innermost stable circular orbit (ISCO) in various models.

Proposal of a conjecture linking Newtonian and relativistic stability points.

Numerical sequences for different mass ratios and adiabatic indices.

Abstract

Quasiequilibrium sequences of binary neutron stars are numerically calculated in the framework of the Isenberg-Wilson-Mathews (IWM) approximation of general relativity. The results are presented for both rotation states of synchronized spins and irrotational motion, the latter being considered as the realistic one for binary neutron stars just prior to the merger. We assume a polytropic equation of state and compute several evolutionary sequences of binary systems composed of different-mass stars as well as identical-mass stars with adiabatic indices gamma=2.5, 2.25, 2, and 1.8. From our results, we propose as a conjecture that if the turning point of binding energy (and total angular momentum) locating the innermost stable circular orbit (ISCO) is found in Newtonian gravity for some value of the adiabatic index gamma_0, that of the ADM mass (and total angular momentum) should exist in the IWM approximation of general relativity for the same value of the adiabatic index.