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Lensing by Kerr Black Holes

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arxiv 1910.12873 v2 pith:3ON3KRAK submitted 2019-10-28 gr-qc astro-ph.HEhep-th

Samuel E. Gralla , Alexandru Lupsasca This is my paper
classification gr-qcastro-ph.HEhep-th
keywords raysbentblackdirectgeneralgeodesicshighlyholes
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abstract

Interpreting horizon-scale observations of astrophysical black holes demands a general understanding of null geodesics in the Kerr spacetime. These may be divided into two classes: "direct" rays that primarily determine the observational appearance of a given source, and highly bent rays that produce a nested sequence of exponentially demagnified images of the main emission: the so-called "photon ring". We develop heuristics that characterize the direct rays and study the highly bent geodesics analytically. We define three critical parameters $\gamma$, $\delta$, and $\tau$ that respectively control the demagnification, rotation, and time delay of successive images of the source, thereby providing an analytic theory of the photon ring. These observable parameters encode universal effects of general relativity, independent of the details of the emitting matter.

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Cited by 7 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Dark matter environments and safeguards for spacetime inference from horizon scale interferometry

    gr-qc 2026-07 conditional novelty 6.0 of 10

    Using public 2017 M87* closure data, a frozen Kerr source fails an absolute adequacy test and the differential tidal-charge response fails numerical convergence, so no posterior or bound is reported.

  2. Critical Behavior of Photon Rings in Kerr-Bertotti-Robinson Spacetime

    gr-qc 2026-03 conditional novelty 6.0 of 10

    For a magnetized Kerr-Bertotti-Robinson black hole, the photon-ring parameters gamma, delta, and tau all decrease compared with the unmagnetized Kerr case, weakening the self-similar stacking of higher-order images.

  3. Photon rings in a holographic toy model

    hep-th 2025-06 conditional novelty 6.0 of 10

    In warped AdS3 black holes, the eikonal quasinormal-mode spectrum is governed exactly by the photon ring's orbital frequency and Lyapunov exponent, with different boundary conditions picking out the outer or inner ring.

  4. Optical Images of the Braneworld Black Hole Surrounded by an Optically Thin Accretion Disk

    astro-ph.HE 2026-07 conditional novelty 5.0 of 10

    A rotating braneworld black hole with tidal charge casts an asymmetric, spin- and q-dependent shadow; with the adopted disk emissivity, its 86 GHz image is brighter than its 230 GHz image.

  5. Semi-analytical Study on the Polarized Images of Black Hole due to Frame Dragging

    gr-qc 2025-08 unverdicted novelty 5.0 of 10

    Frame dragging flips an initially retrograde equatorial flow around a Kerr black hole, and the polarized image shows three distinct critical locations whose spatial hierarchy is derived analytically for an on-axis observer.

  6. Image of the time-dependent black hole

    gr-qc 2025-07 conditional novelty 4.0 of 10

    For a Vaidya black hole with linearly growing mass, the accretion disk image's bright spot shifts radially outward with the conformal time coordinate, while the observed flux in the conformal frame remains time-independent.

  7. Optical images of the Kerr-Sen black hole and thin accretion disk

    gr-qc 2025-07 reject novelty 3.0 of 10

    Ray-traced images of a Kerr-Sen black hole with a thin accretion disk show spin-dominated inner-shadow deformation and inclination-dominated redshift maps, while the 86-versus-230 GHz brightness gap is inherited from ...

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