Towards a Realistic Neutron Star Binary Inspiral: Initial Data and Multiple Orbit Evolution in Full General Relativity

TL;DR

This paper investigates the limitations of the conformally flat quasiequilibrium approach in modeling realistic neutron star binaries in general relativity, emphasizing the need for long-term, high-resolution simulations of full Einstein equations.

Contribution

It critically assesses the validity of CFQE initial data for neutron star binaries and demonstrates the stability of full Einstein simulations for long-term evolution.

Findings

CFQE assumptions violate Einstein equations at large separations

ISCO estimates from CFQE are not astrophysically accurate

Stable long-term simulations of full Einstein equations are feasible

Abstract

This paper reports on our effort in modeling realistic astrophysical neutron star binaries in general relativity. We analyze under what conditions the conformally flat quasiequilibrium (CFQE) approach can generate ``astrophysically relevant'' initial data, by developing an analysis that determines the violation of the CFQE approximation in the evolution of the binary described by the full Einstein theory. We show that the CFQE assumptions significantly violate the Einstein field equations for corotating neutron stars at orbital separations nearly double that of the innermost stable circular orbit (ISCO) separation, thus calling into question the astrophysical relevance of the ISCO determined in the CFQE approach. With the need to start numerical simulations at large orbital separation in mind, we push for stable and long term integrations of the full Einstein equations for the binary neutron star system. We demonstrate the stability of our numerical treatment and analyze the stringent requirements on resolution and size of the computational domain for an accurate simulation of the system.