Binary Neutron Stars in Quasi-equilibrium

TL;DR

This paper constructs quasi-equilibrium models of binary neutron stars with various equations of state, analyzing their orbital dynamics and providing data to guide future numerical simulations of inspiral and merger.

Contribution

It presents a comprehensive set of quasi-equilibrium sequences for binary neutron stars, including unequal-mass cases, and derives empirical formulas for orbital angular velocity at mass-shedding.

Findings

Orbital angular velocity at mass-shedding limit can be empirically estimated.

Tables for 160 sequences are provided as a resource for future simulations.

Behavior of binding energy and angular momentum along sequences is characterized.

Abstract

Quasi-equilibrium sequences of binary neutron stars are constructed for a variety of equations of state in general relativity. Einstein's constraint equations in the Isenberg-Wilson-Mathews approximation are solved together with the relativistic equations of hydrostationary equilibrium under the assumption of irrotational flow. We focus on unequal-mass sequences as well as equal-mass sequences, and compare those results. We investigate the behavior of the binding energy and total angular momentum along a quasi-equilibrium sequence, the endpoint of sequences, and the orbital angular velocity as a function of time, changing the mass ratio, the total mass of the binary system, and the equation of state of a neutron star. It is found that the orbital angular velocity at the mass-shedding limit can be determined by an empirical formula derived from an analytic estimation. We also provide tables for 160 sequences which will be useful as a guideline of numerical simulations for the inspiral and merger performed in the near future.