Numerical Relativity Simulations of Precessing Binary Neutron Star Mergers

TL;DR

This paper presents the first numerical relativity simulations of precessing binary neutron star mergers, analyzing spin dynamics and gravitational waveforms, and assessing the observability of precession effects in different binary orientations.

Contribution

It introduces the first simulations including spin precession effects in binary neutron star mergers with multiple resolutions and detailed waveform analysis.

Findings

Precession effects are detectable in edge-on binaries.

Precession does not significantly alter postmerger frequencies.

Aligned spins are distinguishable from nonspinning configurations.

Abstract

We present the first set of numerical relativity simulations of binary neutron mergers that include spin precession effects and are evolved with multiple resolutions. Our simulations employ consistent initial data in general relativity with different spin configurations and dimensionless spin magnitudes $\sim 0.1$. They start at a gravitational-wave frequency of $\sim392$~Hz and cover more than $1$ precession period and about 15 orbits up to merger. We discuss the spin precession dynamics by analyzing coordinate trajectories, quasi-local spin measurements, and energetics, by comparing spin aligned, antialigned, and irrotational configurations. Gravitational waveforms from different spin configuration are compared by calculating the mismatch between pairs of waveforms in the late inspiral. We find that precession effects are not distinguishable from nonprecessing configurations with aligned spins for approximately face-on binaries, while the latter are distinguishable from a nonspinning configurations. Spin precession effects are instead clearly visible for approximately edge-on binaries. For the parameters considered here, precession does not significantly affect the characteristic postmerger gravitational-wave frequencies nor the mass ejection. Our results pave the way for the modeling of spin precession effects in the gravitational waveform from binary neutron star events.