Lower bound on the radii of circular orbits in the extremal Kerr black-hole spacetime
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866929718785212416 |
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| author | Hod, Shahar |
| author_facet | Hod, Shahar |
| contents | It is often stated in the physics literature that maximally-spinning Kerr black-hole spacetimes are characterized by near-horizon co-rotating circular geodesics of radius $r_{\text{circular}}$ with the property $r_{\text{circular}}\to r^+_{\text{H}}$, where $r_{\text{H}}$ is the horizon radius of the extremal black hole. Based on the famous Thorne hoop conjecture, in the present compact paper we provide evidence for the existence of a non-trivial lower bound ${r_{\text{circular}-r_{\text{H}}}\over{r_{\text{H}}}}\gtrsim (μ/M)^{1/2}$ on the radii of circular orbits in the extremal Kerr black-hole spacetime, where $μ/M$ is the dimensionless mass ratio which characterizes the composed black-hole-orbiting-particle system. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_12244 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Lower bound on the radii of circular orbits in the extremal Kerr black-hole spacetime Hod, Shahar General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena High Energy Physics - Theory It is often stated in the physics literature that maximally-spinning Kerr black-hole spacetimes are characterized by near-horizon co-rotating circular geodesics of radius $r_{\text{circular}}$ with the property $r_{\text{circular}}\to r^+_{\text{H}}$, where $r_{\text{H}}$ is the horizon radius of the extremal black hole. Based on the famous Thorne hoop conjecture, in the present compact paper we provide evidence for the existence of a non-trivial lower bound ${r_{\text{circular}-r_{\text{H}}}\over{r_{\text{H}}}}\gtrsim (μ/M)^{1/2}$ on the radii of circular orbits in the extremal Kerr black-hole spacetime, where $μ/M$ is the dimensionless mass ratio which characterizes the composed black-hole-orbiting-particle system. |
| title | Lower bound on the radii of circular orbits in the extremal Kerr black-hole spacetime |
| topic | General Relativity and Quantum Cosmology High Energy Astrophysical Phenomena High Energy Physics - Theory |
| url | https://arxiv.org/abs/2502.12244 |