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  • Open Access

Looking through the Kerr disk

Maciej Maliborski

Tobias C. Sutter*

  • University of Vienna, Faculty of Mathematics, Oskar-Morgenstern-Platz 1, 1090 Vienna, Austria, University of Vienna, Gravitational Physics, Boltzmanngasse 5, 1090 Vienna, Austria, and TU Wien, Institute of Analysis and Scientific Computing, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria

  • *Contact author: tobias.christoph.sutter@univie.ac.at
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Phys. Rev. D 113, 064002 – Published 2 March, 2026

DOI: https://doi.org/10.1103/s8ps-3zs5

Abstract

We study null geodesics that connect the two asymptotically flat regions of the maximally extended Kerr spacetime. These vortical geodesics traverse both horizons and pass through the ring singularity, linking the positive-r exterior to the negative-r asymptotic side. Using impact parameters, we identify a closed subset of parameter space, the inner throat, where the radial potential has no real roots, and photons exhibit no radial turning points. In this region, at most two constant-latitude geodesics exist, one of which is aligned with the principal null direction. We also identify the forbidden polar-angle band that limits the range of geodesics reaching an asymptotic observer. We solve the geodesic equations analytically and numerically in Eddington-Finkelstein-like coordinates, obtaining mutually consistent results that correct and extend previously available formulas. The resulting trajectories are used to construct simulated views for an observer in the negative-r domain, revealing strong image distortion and inversion, with possible implications for analogous white hole configurations.

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Phys. Rev. D 113, 064002– Published 2 March, 2026
  • Received 23 November 2025
  • Accepted 2 February 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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