Simulations of inspiraling and merging double neutron stars using the Spectral Einstein Code

TL;DR

This paper presents long, accurate general-relativistic simulations of neutron star mergers using the Spectral Einstein Code, improving waveform modeling for gravitational wave analysis and validating results against independent codes.

Contribution

It introduces enhanced numerical methods and mesh refinement techniques in SpEC to produce the longest NSNS merger waveforms to date, aiding gravitational wave data analysis.

Findings

Longest fully relativistic NSNS waveform to date.

Agreement with independent BAM code simulations.

Enhanced mesh refinement improves merger and post-merger resolution.

Abstract

We present results on the inspiral, merger, and post-merger evolution of a neutron star - neutron star (NSNS) system. Our results are obtained using the hybrid pseudospectral-finite volume Spectral Einstein Code (SpEC). To test our numerical methods, we evolve an equal-mass system for $\approx 22$ orbits before merger. This waveform is the longest waveform obtained from fully general-relativistic simulations for NSNSs to date. Such long (and accurate) numerical waveforms are required to further improve semi-analytical models used in gravitational wave data analysis, for example the effective one body models. We discuss in detail the improvements to SpEC's ability to simulate NSNS mergers, in particular mesh refined grids to better resolve the merger and post-merger phases. We provide a set of consistency checks and compare our results to NSNS merger simulations with the independent BAM code. We find agreement between them, which increases confidence in results obtained with either code. This work paves the way for future studies using long waveforms and more complex microphysical descriptions of neutron star matter in SpEC.