Dynamics of scalar fields in the background of rotating black holes II: A note on superradiance

TL;DR

This paper demonstrates that superradiance effects around rotating black holes can be studied through numerical time evolution, but require carefully tuned initial data due to their small amplification effects.

Contribution

It introduces a numerical approach to analyze superradiance in the time domain using a Teukolsky code, highlighting the challenges in detecting such effects.

Findings

Superradiance effects yield less than 1% amplification for scalar pulses.

Careful tuning of initial data is necessary to observe superradiance.

Time domain analysis of superradiance is feasible with specialized numerical methods.

Abstract

We analyze the amplification due to so-called superradiance from the scattering of pulses off rotating black holes as a numerical time evolution problem. We consider the "worst possible case" of scalar field pulses for which superradiance effects yield amplifications $< 1%$. We show that this small effect can be isolated by numerically evolving quasi-monochromatic, modulated pulses with a recently developed Teukolsky code. The results show that it is possible to study superradiance in the time domain, but only if the initial data is carefully tuned. This illustrates the intrinsic difficulties of detecting superradiance in more general evolution scenarios.