Critical Behavior of Photon Rings in Kerr-Bertotti-Robinson Spacetime
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arXiv
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| Main Authors: | , , , , |
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| Format: | Preprint |
| Published: |
2026
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| _version_ | 1866911545265487872 |
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| author | Wan, Xi Zhang, Zhenyu Wei, Fang-Stars Hou, Yehui Chen, Bin |
| author_facet | Wan, Xi Zhang, Zhenyu Wei, Fang-Stars Hou, Yehui Chen, Bin |
| contents | In this work, we investigate the critical behavior of photon rings in the Kerr-Bertotti-Robinson spacetime, describing a rotating black hole immersed in a background magnetic field. We analyze the radial and angular motions of photons under the small magnetic field approximation. Focusing on unstable spherical orbits, we determine three key parameters, $γ$, $δ$, and $τ$, which characterize radial compression, azimuthal advancement, and time delay. We then examine how these parameters depend on the black hole spin, magnetic field strength, and observer inclination for both on-axis and off-axis observers, and we further analyze the properties of higher-order images through near-critical lens equations. The results show that the magnetic field modifies the geodesic structure, and leads to observable changes in the fine structure of photon rings, providing a useful framework for probing magnetized black hole environments. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_25049 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Critical Behavior of Photon Rings in Kerr-Bertotti-Robinson Spacetime Wan, Xi Zhang, Zhenyu Wei, Fang-Stars Hou, Yehui Chen, Bin General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena In this work, we investigate the critical behavior of photon rings in the Kerr-Bertotti-Robinson spacetime, describing a rotating black hole immersed in a background magnetic field. We analyze the radial and angular motions of photons under the small magnetic field approximation. Focusing on unstable spherical orbits, we determine three key parameters, $γ$, $δ$, and $τ$, which characterize radial compression, azimuthal advancement, and time delay. We then examine how these parameters depend on the black hole spin, magnetic field strength, and observer inclination for both on-axis and off-axis observers, and we further analyze the properties of higher-order images through near-critical lens equations. The results show that the magnetic field modifies the geodesic structure, and leads to observable changes in the fine structure of photon rings, providing a useful framework for probing magnetized black hole environments. |
| title | Critical Behavior of Photon Rings in Kerr-Bertotti-Robinson Spacetime |
| topic | General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2603.25049 |