Abstract
We calculate the absorption cross section for planar waves incident upon Kerr black holes, and present a unified picture for scalar, electromagnetic and gravitational waves. We highlight the spin-helicity effect that arises from a coupling between the rotation of the black hole and the helicity of a circularly-polarized wave. For the case of on-axis incidence, we introduce an extended ‘sinc approximation’ to quantify the spin-helicity effect in the strong-field regime.
Highlights
Black holes, once dismissed as a mathematical artifact of Einstein’s theory of general relativity (GR), have come to play a central role in modern astronomy and theoretical physics [1,2]
Black holes pose a challenge: as spacetime curvature grows without bound in GR, the classical theory breaks down
In April 2017, the Event Horizon Telescope (EHT) [6] – a global array of radio telescopes linked by very long baseline interferometry – observed the supermassive black hole candidates Sgr
Summary
Once dismissed as a mathematical artifact of Einstein’s theory of general relativity (GR), have come to play a central role in modern astronomy and theoretical physics [1,2]. The EHT will seek to study the black hole shadow itself [8,9,10], using techniques to surpass the diffraction limit [11]. These experimental advances motivate study of the interaction of electromagnetic waves (EWs) and gravitational waves (GWs). EWs and GWs propagating on curved spacetimes in vacuum share some traits Both possess two independent (transverse) polarizations that are paralleltransported along null geodesics in the ray-optics limit. In the strong-field, we anticipate that waves with a counter-rotating circular polarization are preferentially absorbed (σa−bs > σa+bs)
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