The Final Remnant of Binary Black Hole Mergers: Multipolar Analysis

TL;DR

This paper introduces methods to analyze the multipolar structure of dynamical horizons in numerical relativity, applying them to binary black hole mergers to confirm the final remnant as a Kerr black hole through gauge-invariant and quasinormal mode analysis.

Contribution

It extends multipolar analysis methods to non-axisymmetric dynamical horizons in numerical relativity, enabling detailed characterization of black hole mergers.

Findings

Final remnant is a Kerr black hole.

Methods successfully extract quasinormal modes.

Analysis confirms horizon geometry matches Kerr predictions.

Abstract

Methods are presented to define and compute source multipoles of dynamical horizons in numerical relativity codes, extending previous work from the isolated and dynamical horizon formalisms in a manner that allows for the consideration of horizons that are not axisymmetric. These methods are then applied to a binary black hole merger simulation, providing evidence that the final remnant is a Kerr black hole, both through the (spatially) gauge-invariant recovery of the geometry of the apparent horizon, and through a detailed extraction of quasinormal ringing modes directly from the strong-field region.