Disk illumination by black hole superradiance of electromagnetic perturbations

TL;DR

This paper investigates how electromagnetic superradiance around Kerr black holes can illuminate accretion disks, revealing energy extraction mechanisms and potential hot spot formation.

Contribution

It introduces a Kerr-Schild formalism approach to analyze electromagnetic perturbations and demonstrates energy extraction via superradiance in disk-black hole systems.

Findings

Energy extraction occurs under superradiance conditions.

Negative energy regions exist near the horizon.

Potential hot spots can form on the disk.

Abstract

Using the Kerr-Schild formalism to solve the Einstein-Maxwell equations, we study energy transport due to time-dependent electromagnetic perturbations around a Kerr black hole, which may work as a mechanism to illuminate a disk located on the equatorial plane. For such a disk-hole system it is found that the energy extraction from the hole can occur under the well-known superradiance condition for wave frequency, even though the energy absorption into the hole should be rather dominant near the polar region of the horizon. We estimate the efficiency of the superradiant amplification of the disk illumination. Further we calculate the time-averaged energy density distribution to show explicitly the existence of a negative energy region near the horizon and to discuss the possible generation of a hot spot on the disk.