A post-Newtonian diagnosis of quasiequilibrium configurations of neutron star-neutron star and neutron star-black hole binaries

TL;DR

This paper employs a post-Newtonian diagnostic to evaluate initial data for neutron star binaries, revealing good agreement for double neutron stars and less for neutron star-black hole systems, highlighting residual eccentricity and tidal effects.

Contribution

It introduces a post-Newtonian diagnostic method to assess quasiequilibrium initial data for neutron star binaries, incorporating tidal interactions and comparing with numerical data.

Findings

High accuracy of diagnostic for double neutron star systems

Residual eccentricity may explain discrepancies

Less agreement observed for neutron star-black hole binaries

Abstract

We use a post-Newtonian diagnostic tool to examine numerically generated quasiequilibrium initial data sets for non-spinning double neutron star and neutron star-black hole binary systems. The PN equations include the effects of tidal interactions, parametrized by the compactness of the neutron stars and by suitable values of ``apsidal'' constants, which measure the degree of distortion of stars subjected to tidal forces. We find that the post-Newtonian diagnostic agrees well with the double neutron star initial data, typically to better than half a percent except where tidal distortions are becoming extreme. We show that the differences could be interpreted as representing small residual eccentricity in the initial orbits. In comparing the diagnostic with preliminary numerical data on neutron star-black hole binaries, we find less agreement.