Curvatures, Photon Spheres and Black Hole Shadows

Chen-Kai Qiao

doi:10.1103/PhysRevD.106.084060

paper

Curvatures, Photon Spheres and Black Hole Shadows

arXiv:2208.01771 · doi:10.1103/PhysRevD.106.084060

Abstract

In a recent work PRD 106, L021501 (2022), a new geometric approach is proposed to obtain the photon sphere (circular photon orbit) and the black hole shadow radius. In this approach, photon spheres and the black hole shadow radius are determined using geodesic curvature and Gaussian curvature in the optical geometry of black hole spacetimes. However, the calculations in PRD 106, L021501 (2022) only restricted to a subclass of static and spherically symmetric black holes with spacetime metric $g_{tt} \cdot g_{r r} = - 1$ , $g_{θ θ} = r^{2}$ and $g_{ϕϕ} = r^{2} sin^{2} θ$ . In this work, we extend this approach to more general spherically symmetric black holes (with spacetime metric $d s^{2} = g_{tt} d t^{2} + g_{r r} d r^{2} + g_{θ θ} d θ^{2} + g_{ϕϕ} d ϕ^{2}$ ). Furthermore, it can be proved that our results from the geometric approach are completely equivalent to those from conventional approach based on effective potentials of test particles.

arXiv comment14 pages, 3 figures, 3 tables (text overlap with arXiv:2204.07297). V2: Minor Revision, Accepted by Physical Review D

Curvatures, Photon Spheres and Black Hole Shadows

Abstract

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