A hybrid method for understanding black-hole mergers: head-on case

TL;DR

This paper introduces a hybrid approach combining post-Newtonian and black-hole perturbation theories to model head-on black-hole mergers, showing good agreement with numerical simulations and capturing key gravitational wave features.

Contribution

The paper presents a novel hybrid method integrating PN and BHP theories specifically for head-on black-hole mergers, enhancing analytical modeling accuracy.

Findings

Hybrid method matches numerical relativity waveforms

Good agreement in radiated energy and momentum

Linear perturbation theories can capture nonlinear merger features

Abstract

Black-hole-binary coalescence is often divided into three stages: inspiral, merger and ringdown. The post-Newtonian (PN) approximation treats the inspiral phase, black-hole perturbation (BHP) theory describes the ringdown, and the nonlinear dynamics of spacetime characterize the merger. In this paper, we introduce a hybrid method that incorporates elements of PN and BHP theories, and we apply it to the head-on collision of black holes with transverse, anti-parallel spins. We compare our approximation technique with a full numerical-relativity simulation, and we find good agreement between the gravitational waveforms and the radiated energy and momentum. Our results suggest that PN and BHP theories may suffice to explain the main features of outgoing gravitational radiation for head-on mergers. This would further imply that linear perturbations to exact black-hole solutions can capture the nonlinear aspects of head-on binary-black-hole mergers accessible to observers far from the collision.