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Black holes typically inhabit highly dynamical galactic environments and arefrequently permeated by accretion media. The inevitable scattering of scalar,electromagnetic and gravitational waves off rotating and charged black holesprovides a remarkable demonstration of the energy extraction and subsequentamplification of scattered waves under the expense of the compact object'srotational and electromagnetic energy; a phenomenon known as superradiance.Certain circumstances tremendously favor the energy extraction process in suchextent that linear superradiant instabilities are triggered. We examine thesuperradiant amplification of monochromatic charged scalar fields impingingReissner-Nordstr\"om-de Sitter black holes which are known to exhibitsuperradiantly unstable quasinormal modes. We find that even though thefrequency range of superradiance is reduced when a positive cosmologicalconstant is incorporated, the amplification factors are significantly elevatedwith respect to those occurring in Reissner-Nordstr\"om spacetime.Intriguingly, we confirm that the long-lived quasinormal resonances that residein the superradiant regime induce resonant peaks when the wave's frequencymatches the real part of the quasinormal mode, regardless of the spacetime'smodal stability.

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