Spin-induced Scalar Clouds around Kerr-Newman Black Holes

TL;DR

This paper constructs and analyzes spin-induced scalar clouds around Kerr-Newman black holes, revealing the importance of strong coupling and rotation rates for their existence and characteristics.

Contribution

It provides the first detailed construction of scalar clouds for Kerr-Newman black holes, including both fundamental and excited modes, and explores their existence conditions.

Findings

Scalar clouds require strong scalar-electromagnetic coupling.

Slow or rapid black hole rotation prevents scalar cloud formation.

Scalar cloud wave functions are concentrated near the black hole poles.

Abstract

Recent studies have demonstrated that a scalar field non-minimally coupled to the electromagnetic field can experience a spin-induced tachyonic instability near Kerr-Newman black holes, potentially driving the formation of scalar clouds. In this paper, we construct such scalar clouds for both fundamental and excited modes, detailing their existence domains and wave functions. Our results indicate that a sufficiently strong coupling between the scalar and electromagnetic fields is essential for sustaining scalar clouds. Within the strong coupling regime, black holes that rotate either too slowly or too rapidly are unable to support scalar clouds. Furthermore, we observe that scalar cloud wave functions are concentrated near the black hole's poles. These findings provide a foundation for future investigations of spin-induced scalarized Kerr-Newman black holes.