Insights into Binary Neutron Star Merger Simulations: A Multi-Code Comparison

TL;DR

This paper compares five leading numerical relativity codes for simulating binary neutron star mergers, analyzing their accuracy, convergence, and the impact of physical parameters on gravitational wave predictions to improve future simulation reliability.

Contribution

It provides a comprehensive multi-code comparison of BNS merger simulations, introduces a novel quasi-universal relation for post-merger dynamics, and assesses the influence of the equation of state on waveforms.

Findings

Codes show general agreement but have discrepancies in post-merger phase.

Discretization errors vary across codes and impact waveform accuracy.

Tidal interactions significantly affect key GW spectral features.

Abstract

Gravitational Wave (GW) signals from Binary Neutron Star (BNS) mergers provide critical insights into the properties of matter under extreme conditions. Due to the scarcity of observational data, Numerical Relativity (NR) simulations are indispensable for exploring these phenomena. However, simulating BNS mergers is a formidable challenge, and ensuring the consistency, reliability or convergence, especially in the post-merger, remains a work in progress. In this paper we assess the performance of current BNS merger simulations by analyzing open-source GW waveforms from five leading NR codes - SACRA, BAM, THC, Whisky amd SpEC. We focus on the accuracy of these simulations and on the effect of the equation of state (EOS) on waveform predictions. We first check if different codes give similar results for similar initial data, then apply two methods to calculate convergence and quantify discretization errors. Lastly, we perform a thorough investigation into the effect of tidal interactions on key frequencies in the GW spectrum. We introduce a novel quasi-universal relation for the transient post-merger time, enhancing our understanding of remnant dynamics in this region. This detailed analysis clarifies agreements and discrepancies between these leading NR codes, and highlights necessary improvements for the advanced accuracy requirements of future GW detectors.