New code for quasiequilibrium initial data of binary neutron stars: Corotating, irrotational and slowly spinning systems

TL;DR

This paper extends a computational code to generate initial data for binary neutron star systems with various spins, validating it against existing methods and exploring a wide range of physical parameters.

Contribution

The authors develop and validate a new code for constructing quasiequilibrium initial data of binary neutron stars with different spin configurations, including highly relativistic cases.

Findings

The new code accurately reproduces known solutions with 0.05% precision.

It can handle a wide range of compactness from white dwarf to neutron star binaries.

Equilibria for spinning neutron stars with realistic equations of state are presented.

Abstract

We present the extension of our \cocal~- Compact Object CALculator - code to compute general-relativistic initial data for binary compact-star systems. In particular, we construct quasiequilibrium initial data for equal-mass binaries with spins that are either aligned or antialigned with the orbital angular momentum. The Isenberg-Wilson-Mathews formalism is adopted and the constraint equations are solved using the representation formula with a suitable choice of a Green's function. We validate the new code with solutions for equal-mass binaries and explore its capabilities for a wide range of compactnesses, from a white dwarf binary with compactness $\sim 10^{-4}$, up to a highly relativistic neutron-star binary with compactness $\sim 0.22$. We also present a comparison with corotating and irrotational quasiequilibrium sequences from the spectral code \lorene [Taniguchi and Gourgoulhon, Phys. Rev. D {\bf 66}, 104019 (2002)] and with different compactness, showing that the results from the two codes agree to a precision of the order of $0.05\%$. Finally, we present equilibria for spinning configurations with a nuclear-physics equation of state in a piecewise polytropic representation.