Scalar clouds and the superradiant instability regime of Kerr-Newman black hole

TL;DR

This paper analyzes the conditions under which massive charged scalar fields form clouds and induce superradiant instability around Kerr-Newman black holes, providing criteria to predict such phenomena.

Contribution

It introduces a parameter space partitioning method to identify regions where scalar clouds and superradiant instability can occur around Kerr-Newman black holes.

Findings

Superradiant instability occurs only in specific parameter space regions.

Scalar clouds have bounded mass and charge within limited regions.

The results enable quick assessment of instability and cloud formation likelihood.

Abstract

In this paper, we study a physical system that is composed of massive charged scalar field linearly coupled to a charged rotating Kerr-Newman black hole. Given the parameters of black hole and a specific set of "quantum" numbers, the parameter space of the scalar field, which is a plane spanned by its mass and charge, is divided into five partitions by three simple constraint lines and the existence line of scalar clouds. The physical properties of the system in these partitions are presented. It is found that superradiant instability may be possibly caused only in two of the partitions. In particular, it is shown that both the mass and charge of the scalar clouds are bounded in a limited region. Our results may be used to rapidly judge the possible occurrence of superradiant instability and the existence of scalar clouds around a given black hole.