Halted-Pendulum Relaxation: Application to White Dwarf Binary Initial Data

TL;DR

This paper introduces Halted-Pendulum Relaxation (HPR), a new method to efficiently prepare initial conditions for SPH simulations of white dwarf binaries, improving accuracy and reducing oscillations.

Contribution

The paper presents HPR, a simple and effective relaxation technique for SPH particles, enhancing the accuracy of initial conditions in binary star merger simulations.

Findings

HPR effectively removes global oscillations in SPH configurations.

HPR improves the accuracy of initial conditions for white dwarf binary simulations.

HPR leads to more realistic orbital and accretion dynamics.

Abstract

Studying compact star binaries and their mergers is integral to determining progenitors for observable transients. Today, compact-star mergers are typically studied via state-of-the-art computational fluid dynamics codes. One such numerical technique, Smoothed Particle Hydrodynamics (SPH), is frequently chosen for its excellent mass, energy, and momentum conservation. The natural treatment of vacuum and the ability to represent highly irregular morphologies make SPH an excellent tool for the study of compact-star binaries and mergers. For many scenarios, including binary systems, the outcome of simulations is only as accurate as the initial conditions. For SPH, it is essential to ensure that the particles are distributed regularly, representing the initial density profile but without long-range correlations. Particle noise in the form of high-frequency local motion and low-frequency global dynamics must be damped out. Damping the latter can be as computationally intensive as the actual simulation. We discuss a new and straightforward relaxation method, Halted-Pendulum Relaxation (HPR), to remove global oscillation modes of SPH particle configurations. In combination with effective external potentials representing gravitational and orbital forces, we show that HPR has an excellent performance in efficiently relaxing SPH particles to the desired density distribution and removing global oscillation modes. We compare the method to frequently used relaxation approaches and test it on a white dwarf binary model at its Roche lobe overflow limit. We highlight the importance of our method in achieving accurate initial conditions and its effect on achieving circular orbits and realistic accretion rates when compared with other general relaxation methods.