Quasiequilibrium states of black hole-neutron star binaries in the moving-puncture framework

TL;DR

This paper computes and compares quasiequilibrium states of black hole-neutron star binaries using the moving-puncture framework, finding good agreement with other methods at certain parameters and proposing improvements to reduce eccentricity.

Contribution

It introduces three conditions for quasiequilibrium states in the moving-puncture framework and demonstrates their effectiveness compared to the excision framework and post-Newtonian approximations.

Findings

Results agree with excision framework and post-Newtonian approximation at specific parameters.

Deviations occur at higher orbital velocities, indicating non-quasicircular states.

Moving-puncture method can produce states with lower eccentricity than other approaches.

Abstract

General relativistic quasiequilibrium states of black hole-neutron star binaries are computed in the moving-puncture framework. We propose three conditions for determining the quasiequilibrium states and compare the numerical results with those obtained in the excision framework. We find that the results obtained in the moving-puncture framework agree with those in the excision framework and with those in the third post-Newtonian approximation for the cases that (i) the mass ratio of the binary is close to unity irrespective of the orbital separation, and (ii) the orbital separation is large enough ($m_0\Omega \alt 0.02$ where $m_0$ and $\Omega$ are the total mass and the orbital angular velocity, respectively) irrespective of the mass ratio. For $m_0 \Omega \agt 0.03$, both of the results in the moving-puncture and excision frameworks deviate, more or less, from those in the third post-Newtonian approximation. Thus the numerical results do not provide a quasicircular state, rather they seem to have a nonnegligible eccentricity of order 0.01--0.1. We show by numerical simulation that a method in the moving-puncture framework can provide approximately quasicircular states in which the eccentricity is by a factor of $\sim 2$ smaller than those in quasiequilibrium given by other approaches.