Wada structures in a binary black hole system

TL;DR

This paper investigates the complex fractal structures of binary black hole shadows, revealing Wada properties using nonlinear dynamics techniques, which enhances understanding of their boundary behaviors.

Contribution

It introduces a novel application of nonlinear dynamics algorithms to identify Wada properties in binary black hole shadows, advancing the analysis of their fractal boundary structures.

Findings

Binary black hole shadows exhibit Wada boundary properties.

The developed algorithm distinguishes fractal from regular shadow regions.

Fractal structures in shadows relate to nonlinear dynamical systems.

Abstract

A key goal of the Event Horizon Telescope is to observe the shadow cast by a black hole. Recent simulations have shown that binary black holes, the progenitors of gravitational waves, present shadows with fractal structure. Here we study the binary shadow structure using techniques from nonlinear dynamics, recognising shadows as exit basins of open Hamiltonian dynamical systems. We apply a recently developed numerical algorithm to demonstrate that parts of the Majumdar-Papapetrou binary black hole shadow exhibit the Wada property: any point of the boundary of one basin is also on the boundary of at least two additional basins. We show that the algorithm successfully distinguishes between the fractal and regular (i.e., non-fractal) parts of the binary shadow.