Highly accurate simulations of asymmetric black-hole scattering and cross validation of effective-one-body models

TL;DR

This paper presents 60 new high-precision numerical relativity simulations of black-hole scattering, compares them with various effective-one-body models, and highlights the first measurement of asymmetric gravitational-wave emission effects on scattering angles.

Contribution

It provides the first direct comparison of NR scattering angles across different codes and with EOB models, including the first measurement of asymmetry effects due to gravitational-wave emission.

Findings

NR simulations agree well across codes for scattering angles

EOB models generally match NR results within 8-5% depending on the model

Asymmetric gravitational-wave emission causes measurable differences in scattering angles

Abstract

The study of unbound binary-black-hole encounters provides a gauge-invariant approach to exploring strong-field gravitational interactions in two-body systems, which can subsequently inform waveform models for bound orbits. In this work, we present 60 new highly accurate numerical relativity (NR) simulations of black-hole scattering, generated using the Spectral Einstein Code (SpEC). Our simulations include 14 spin-aligned configurations, as well as 16 configurations with unequal masses, up to a mass ratio of 10. We perform the first direct comparison of scattering angles computed using different NR codes, finding good agreement. We compare our NR scattering angle results to the post-Minkowskian (PM)-based effective-one-body (EOB) closed-form models SEOB-PM and $w_{\rm EOB}$, finding less than 5% deviation except near the scatter-capture separatrix. Comparisons with the post-Newtonian-based EOB evolution models SEOBNRv5 and TEOBResumS-Dal\'{i} reveal that the former agrees within 8% accuracy with non-spinning NR results across most parameter ranges, whereas the latter matches similarly at lower energies but diverges significantly at higher energies. Both evolution EOB models exhibit increased deviations for spinning systems, predicting a notably different location of the capture separatrix compared to NR. Our key result is the first measurement of disparate scattering angles from NR simulations due to asymmetric gravitational-wave emission. We compare these results to SEOB-PM models constructed to calculate the scattering angle of a single black hole in asymmetric systems.