Scalar absorption by charged rotating black holes

Abstract

We compute numerically the absorption cross section of planar massless scalar waves impinging upon a Kerr-Newman black hole with different incidence angles. We investigate the influence of the black hole electric charge and angular momentum in the absorption spectrum, comparing our numerical computations with analytical results for the limits of high and low frequency.Comment: Accepted for publication in Physical Review

On-axis tidal forces in Kerr spacetime

“…We find that both δr (1) and δr (2) satisfy the geodesic deviation equation (49) for η2. However, these do not describe geodesic deviation but the deviation of the radial coordinate.…”

“…We note that, in the limit θ → 0 with θ > 0, the vectors e µ (0) , e µ (1) , e µ (2) and −e µ (3) point in the directions of increasing t, r, θ and φ, respectively. As a result, the Carter tetrad on the geodesic along the rotation axis rotates with the angular velocity given by φ in Eq.…”

“…The radial component of the deviation vector satisfying the IC1 is proportional to δr (2) and is given by…”

“…The Kerr spacetime is one example of such rotating solutions, which describes the geometry around electrically uncharged and rotating BHs. These fully collapsed structures with non-vanishing angular momentum can be associated to many interesting features in absorption [2][3][4][5][6][7] and scattering [6,8,9] of fields and superradiant instabilities [10,11].…”

On-axis scattering of scalar fields by charged rotating black holes

“…Another key feature of scattering by BHs is superradiance [29], which allows low-frequency waves to experience an amplification, while the BH suffers a decrease in its parameters. This effect implies in a reflection coefficient greater than the unity, within the superradiance threshold, what accounts for a negative absorption cross section [30][31][32].…”