Charged black holes in de Sitter space: Superradiant amplification of charged scalar waves and resonant hyperradiation

Abstract

Black holes typically inhabit highly dynamical galactic environments and are frequently permeated by accretion media. The inevitable scattering of scalar, electromagnetic and gravitational waves off rotating and charged black holes provides a remarkable demonstration of the energy extraction and subsequent amplification of scattered waves under the expense of the compact object's rotational and electromagnetic energy; a phenomenon known as superradiance. Certain circumstances tremendously favor the energy extraction process in such extent that linear superradiant instabilities are triggered. We examine the superradiant amplification of monochromatic charged scalar fields impinging Reissner-Nordström-de Sitter black holes which are known to exhibit superradiantly unstable quasinormal modes. We find that even though the frequency range of superradiance is reduced when a positive cosmological constant is incorporated, the amplification factors are significantly elevated with respect to those occurring in Reissner-Nordström spacetime. Intriguingly, we confirm that the long-lived quasinormal resonances that reside in the superradiant regime induce resonant peaks when the wave's frequency matches the real part of the quasinormal mode, regardless of the spacetime's modal stability.

Dynamical behavior of the $C$-metric: charged scalar fields, quasinormal modes and superradiance

“…This does not guarantee that the phenomenon of superradiance does not occur in such spacetimes (we tackle this investigation on the following subsection). Nonetheless, these results contrast those found in RNdS BHs, where charged scalar perturbations are superradiantly unstable [93][94][95] and lead to resonant hyperradiation with the amplification factors reaching very high levels close to superradiant QNMs [96].…”

“…6 we confirm that a favorable combination of acceleration and charge coupling maximizes the amplification such that Z 0 → 100%, though our numerical investigation entails that the charge coupling is more efficient in the maximization of superradiance than the acceleration. Nevertheless, the increment of αM diminishes the frequency range for which accelerating BHs superradiate, in similarity with Kerr-dS [97] and RNdS BHs [96].…”

“…The acceleration horizon that is generally present in such spacetimes shares many similarities with the cosmological horizon of de Sitter BHs and the overall causal structure of the charged C-metric resembles that of RNdS geometries. Due to the existence of QNM instabilities [93][94][95], as well as the presence of superradiant hyperradiation in RNdS BHs against charged scalar fields [96], an analogous investigation of these phenomena in charged accelerating BHs is of interest.…”

Pseudospectrum of horizonless compact objects: A bootstrap instability mechanism

“…Potential future works in this direction include introducing this methodology to a wider range of BH and ECO setups, with different asymptotic structures and symmetries (see e.g. [32,33,91,98,[105][106][107][108]).…”

An implementation of the matrix method using Chebyshev grid

“…More recently, the method was generalized [31] to the potentials containing discontinuity and aimed to the higher orders [32]. The approach provides reasonable accuracy and efficiency and has been utilized in various studies [6,[34][35][36][37][38][39][40][41][42][43][44][45][46].…”