Exploring the Dynamics of General Relativistic Binary-Single and Binary-Binary Encounters of Black Holes

TL;DR

This study uses the BAM numerical-relativity code to simulate complex relativistic encounters of black holes, revealing unique gravitational-wave signals and dynamics that differ from post-Newtonian predictions.

Contribution

It demonstrates the first detailed simulations of binary-single and binary-binary black hole encounters with fully relativistic dynamics using BAM.

Findings

Simulations show diverse dynamical outcomes including mergers and exchanges.

Gravitational waveforms have distinctive features potentially observable.

Relativistic dynamics differ significantly from post-Newtonian approximations.

Abstract

In this exploratory study, we demonstrate the capability of the numerical-relativity code BAM to simulate fully relativistic black-hole binary-single and binary-binary encounters. While previous work has demonstrated the general capability of numerical-relativity frameworks to evolve spacetimes with $N$ black holes, detailed explorations of such encounters remain limited. We focus on scenarios involving initially non-spinning, equal-mass black holes that result in a variety of dynamical outcomes, including flybys, delayed or accelerated eccentric mergers, exchanges, and more complex interactions. Our results show that we can reliably simulate scattering experiments involving three and four black holes, which exhibit interesting dynamics and gravitational-wave signals. The dynamics of these systems show noticeable differences compared to analogous systems in post-Newtonian approximations up to 2.5PN. A key result is that the gravitational waveforms exhibit remarkable features that could potentially make them distinguishable from regular binary mergers.