Initial data for black hole-neutron star binaries: a flexible, high-accuracy spectral method

TL;DR

This paper introduces a high-accuracy spectral numerical scheme for generating initial data of black hole-neutron star binaries, improving precision and flexibility over previous methods, and enabling the modeling of more realistic astrophysical systems.

Contribution

The authors develop a novel spectral method that achieves high accuracy and flexibility in constructing initial data for black hole-neutron star binaries, including spinning black holes and low-eccentricity orbits.

Findings

Method converges rapidly for isolated neutron stars.

Small inconsistencies in quasi-equilibrium binaries are significantly reduced.

Able to generate diverse initial data configurations.

Abstract

We present a new numerical scheme to solve the initial value problem for black hole-neutron star binaries. This method takes advantage of the flexibility and fast convergence of a multidomain spectral representation of the initial data to construct high-accuracy solutions at a relatively low computational cost. We provide convergence tests of the method for both isolated neutron stars and irrotational binaries. In the second case, we show that we can resolve the small inconsistencies that are part of the quasi-equilibrium formulation, and that these inconsistencies are significantly smaller than observed in previous works. The possibility of generating a wide variety of initial data is also demonstrated through two new configurations inspired by results from binary black holes. First, we show that choosing a modified Kerr-Schild conformal metric instead of a flat conformal metric allows for the construction of quasi-equilibrium binaries with a spinning black hole. Second, we construct binaries in low-eccentricity orbits, which are a better approximation to astrophysical binaries than quasi-equilibrium systems.