Generic Tracking of Multiple Apparent Horizons with Level Flow

TL;DR

This paper introduces a novel level-flow method for locating multiple apparent horizons in complex black hole spacetimes, capable of handling topology changes and independent of initial guess, demonstrated in binary black hole simulations.

Contribution

The paper presents the first apparent horizon locator that can find multiple horizons in generic black hole spacetimes using a topology-changing level-flow approach.

Findings

Successfully tracked multiple horizons in binary black hole simulations

Method is independent of initial guess and can handle topology changes

Demonstrated robustness in Kerr-Schild binary black hole scenarios

Abstract

We report the development of the first apparent horizon locator capable of finding multiple apparent horizons in a ``generic'' numerical black hole spacetime. We use a level-flow method which, starting from a single arbitrary initial trial surface, can undergo topology changes as it flows towards disjoint apparent horizons if they are present. The level flow method has two advantages: 1) The solution is independent of changes in the initial guess and 2) The solution can have multiple components. We illustrate our method of locating apparent horizons by tracking horizon components in a short Kerr-Schild binary black hole grazing collision.