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arXiv · 2106.09731

Conversion of electromagnetic and gravitational waves by a charged black hole

Mohamed Ould El Hadj·Sam R. Dolan
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Abstract

In a strong electromagnetic field, gravitational waves are converted into electromagnetic waves of the same frequency, and vice versa. Here we calculate the scattering and conversion cross sections for a planar wave impinging upon a Reissner-Nordstr\"om black hole in vacuum, using the partial-wave expansion and numerical methods. We show that, at long wavelengths, the conversion cross section matches that computed by Feynman-diagram techniques. At short wavelengths, the essential features are captured by a geometric-optics approximation. We demonstrate that the converted flux can exceed the scattered flux at large scattering angles, for highly-charged black holes. In the short-wavelength regime, the conversion effect may be understood in terms of a phase that accumulates along a ray. We compute the scattering angle for which the converted and scattered fluxes are equal, as a function of charge-to-mass ratio. We show that this scattering angle approaches $90$ degrees in the extremal limit.

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BibTeXRIS

Mohamed Ould El Hadj, Sam R. Dolan. 2021-06-17. Conversion of electromagnetic and gravitational waves by a charged black hole. https://doi.org/10.1103/physrevd.106.044002

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