Shadow of rotating black holes with consistent thermodynamics
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866911452852387840 |
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| author | Chen, Che-Yu Chen, Chiang-Mei Ohta, Nobuyoshi |
| author_facet | Chen, Che-Yu Chen, Chiang-Mei Ohta, Nobuyoshi |
| contents | Quantum effects in general induce scale dependence in the coupling constants. We explore this possibility in gravity, with a scale-dependent Newton coupling. When applied to Kerr black holes with such a running coupling, the consistency of black hole thermodynamics requires that the Newton coupling have a specific dependence on the black hole parameters. In this work, we consider such a class of Newton couplings and look for the possible observational implications on the highly lensed images of the black holes. In addition to placing constraints on the parameter space of the model through the latest Sgr A* images, we find that the variations in the shape of shadows in a large portion of the parameter space can be qualitatively captured by a quantity solely defined by the event horizon. Most importantly, the consistency of thermodynamics suggests a lower bound on the shadow size, beyond which either horizon disappears, or the shadow cannot keep the standard D-shaped structure. The possibility that the black holes in this model could spin faster than the Kerr bound, and the physical implications of the resulting cuspy shadows, are also discussed. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_00708 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Shadow of rotating black holes with consistent thermodynamics Chen, Che-Yu Chen, Chiang-Mei Ohta, Nobuyoshi General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena High Energy Physics - Phenomenology High Energy Physics - Theory Quantum effects in general induce scale dependence in the coupling constants. We explore this possibility in gravity, with a scale-dependent Newton coupling. When applied to Kerr black holes with such a running coupling, the consistency of black hole thermodynamics requires that the Newton coupling have a specific dependence on the black hole parameters. In this work, we consider such a class of Newton couplings and look for the possible observational implications on the highly lensed images of the black holes. In addition to placing constraints on the parameter space of the model through the latest Sgr A* images, we find that the variations in the shape of shadows in a large portion of the parameter space can be qualitatively captured by a quantity solely defined by the event horizon. Most importantly, the consistency of thermodynamics suggests a lower bound on the shadow size, beyond which either horizon disappears, or the shadow cannot keep the standard D-shaped structure. The possibility that the black holes in this model could spin faster than the Kerr bound, and the physical implications of the resulting cuspy shadows, are also discussed. |
| title | Shadow of rotating black holes with consistent thermodynamics |
| topic | General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2510.00708 |