One-dimensional linear analysis and numerical simulations of Alfven waves in a force-free magnetosphere around a Kerr black hole

TL;DR

This paper investigates the propagation and energy transport of Alfven waves in a force-free magnetosphere around a Kerr black hole through linear analysis and simulations, revealing wave interactions and reflection phenomena.

Contribution

It provides a detailed analysis of Alfven wave behavior in a Kerr black hole environment, including wave-induced magnetosonic waves and reflection effects, extending previous studies.

Findings

Alfven waves induce magnetosonic waves in a spinning black hole magnetosphere.

Energy conservation holds when including the induced magnetosonic waves.

Reflection of inward Alfven waves occurs near the static limit, contrary to eikonal approximation predictions.

Abstract

We perform one-dimensional linear analysis and numerical simulations of the propagation of Alfven waves in a force-free magnetosphere along magnetic field lines around a spinning black hole. We use the results to investigate the dynamic process of wave propagation and energy transport for Alfven waves. As in a previous study using the Banados--Teitelboim--Zanelli spacetime (Koide et al. 2022), the Alfven wave induces a fast magnetosonic wave in the case of a spinning black hole. Energy conservation is confirmed when this additional induced magnetosonic wave is considered. We also observe the reflection of the inwardly propagating Alfven wave around the static limit, which is prohibited in theory when using the eikonal approximation.