Primary caustics and critical points behind a Kerr black hole
- Institut fuer Theoretische Physik, Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland)
The primary optical caustic surface behind a Kerr black hole is a four-cusped tube displaced from the line of sight. We derive the caustic surface in the nearly asymptotic region far from the black hole through a Taylor expansion of the lightlike geodesics up to and including fourth-order terms in m/b and a/b, where m is the black hole mass, a the spin, and b the impact parameter. The corresponding critical locus in the observer's sky is elliptical and a pointlike source inside the caustics will be imaged as an Einstein cross. With regard to lensing near critical points, a Kerr lens is analogous to a circular lens perturbed by a dipole and a quadrupole potential. The caustic structure of the supermassive black hole in the Galactic center could be probed by lensing of low mass x-ray binaries in the galactic inner regions or by hot spots in the accretion disk.
- OSTI ID:
- 21250312
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 78, Issue 2; Other Information: DOI: 10.1103/PhysRevD.78.023008; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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