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Title: Optical caustics of Kerr spacetime: The full structure

Abstract

I present an exhaustive numerical investigation of the optical caustics in gravitational lensing by a spinning black hole for an observer at infinity. Besides the primary caustic, I examine higher order caustics, formed by photons performing one or several loops around the black hole. My investigation covers the whole parameter space, including the black hole spin, its inclination with respect to the line of sight, the source distance, and the caustic order. By comparing my results with the available analytical approximations, I find perfect agreement in their respective domains of validity. I then prove that all caustics maintain their shape (a tube with astroidal cross section) in the entire parameter space without suffering any transitions to different caustic shapes. For nearly extremal spin, however, higher order caustics grow so large that their cross sections at fixed radii wind several times around the black hole. As a consequence, for each caustic order, the number of images ranges from 2 to 2(n+1), where n is the number of loops spanned by the caustic. As for the critical curves, I note that for high values of the spin they develop a small dip on the side corresponding to prograde orbits.

Authors:
 [1]
  1. Dipartimento di Fisica 'E.R. Caianiello', Universita di Salerno, via Allende, I-84081 Baronissi (Italy)
Publication Date:
OSTI Identifier:
21250808
Resource Type:
Journal Article
Journal Name:
Physical Review. D, Particles Fields
Additional Journal Information:
Journal Volume: 78; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevD.78.063014; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0556-2821
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; APPROXIMATIONS; BLACK HOLES; CROSS SECTIONS; GRAVITATIONAL LENSES; KERR EFFECT; KERR FIELD; MAGNETO-OPTICAL EFFECTS; PHOTONS; SPACE; SPACE-TIME; SPIN

Citation Formats

Bozza, V, and Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli. Optical caustics of Kerr spacetime: The full structure. United States: N. p., 2008. Web. doi:10.1103/PHYSREVD.78.063014.
Bozza, V, & Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli. Optical caustics of Kerr spacetime: The full structure. United States. https://doi.org/10.1103/PHYSREVD.78.063014
Bozza, V, and Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli. 2008. "Optical caustics of Kerr spacetime: The full structure". United States. https://doi.org/10.1103/PHYSREVD.78.063014.
@article{osti_21250808,
title = {Optical caustics of Kerr spacetime: The full structure},
author = {Bozza, V and Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli},
abstractNote = {I present an exhaustive numerical investigation of the optical caustics in gravitational lensing by a spinning black hole for an observer at infinity. Besides the primary caustic, I examine higher order caustics, formed by photons performing one or several loops around the black hole. My investigation covers the whole parameter space, including the black hole spin, its inclination with respect to the line of sight, the source distance, and the caustic order. By comparing my results with the available analytical approximations, I find perfect agreement in their respective domains of validity. I then prove that all caustics maintain their shape (a tube with astroidal cross section) in the entire parameter space without suffering any transitions to different caustic shapes. For nearly extremal spin, however, higher order caustics grow so large that their cross sections at fixed radii wind several times around the black hole. As a consequence, for each caustic order, the number of images ranges from 2 to 2(n+1), where n is the number of loops spanned by the caustic. As for the critical curves, I note that for high values of the spin they develop a small dip on the side corresponding to prograde orbits.},
doi = {10.1103/PHYSREVD.78.063014},
url = {https://www.osti.gov/biblio/21250808}, journal = {Physical Review. D, Particles Fields},
issn = {0556-2821},
number = 6,
volume = 78,
place = {United States},
year = {Mon Sep 15 00:00:00 EDT 2008},
month = {Mon Sep 15 00:00:00 EDT 2008}
}