Photon Rings and Mass-Independent Observables of a Five-Dimensional Charged AdS Black Hole
Abstract
We investigate the optical properties of a five-dimensional charged anti-de Sitter (AdS) black hole. Using the null geodesic equations, we determine the event horizon and photon sphere radii and the critical impact parameter, showing that all decrease with increasing charge, while the photon sphere radius remains independent of the AdS radius. To avoid dependence on the mass scale and the observer-dependent apparent size of the shadow in an AdS spacetime, we introduce two mass-independent geometric observables: the subring exponent γ and the ratio of the critical impact parameter to that of the direct image of the innermost stable circular orbit (ISCO). We derive γ in closed form and show that it is independent of the AdS radius and satisfies 2π/√3<γ≤π√2, above the values for four-dimensional Schwarzschild and Reissner--Nordström black holes. Using a Markov chain Monte Carlo (MCMC) forecast based on noiseless mock data with illustrative fractional uncertainties of 5%, we find that the dimensionless AdS radius can be constrained with a relative uncertainty of $16−−19\%$, whereas the charge can be distinguished from zero only for the near-extremal fiducial model considered. Under these assumptions, the subring exponent provides a Gaussian separation of $3.4−−5.9σ$ from the four-dimensional Schwarzschild black hole.
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BibTeX
@misc{mamatkhonov2026photon,
title = {{Photon Rings and Mass-Independent Observables of a Five-Dimensional Charged AdS Black Hole}},
author = {Amrillokhon Mamatkhonov and Javokhir Sharipov and Tursunali Xamidov and Chen Zhou and Sanjar Shaymatov and Chengxun Yuan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40069},
eprint = {2610.40069},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40069},
}
RIS
TY - UNPB
TI - Photon Rings and Mass-Independent Observables of a Five-Dimensional Charged AdS Black Hole
AU - Amrillokhon Mamatkhonov
AU - Javokhir Sharipov
AU - Tursunali Xamidov
AU - Chen Zhou
AU - Sanjar Shaymatov
AU - Chengxun Yuan
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40069
UR - https://arxiv.org/abs/2610.40069
AB - We investigate the optical properties of a five-dimensional charged anti-de Sitter (AdS) black hole. Using the null geodesic equations, we determine the event horizon and photon sphere radii and the critical impact parameter, showing that all decrease with increasing charge, while the photon sphere radius remains independent of the AdS radius. To avoid dependence on the mass scale and the observer-dependent apparent size of the shadow in an AdS spacetime, we introduce two mass-independent geometric observables: the subring exponent γ and the ratio of the critical impact parameter to that of the direct image of the innermost stable circular orbit (ISCO). We derive γ in closed form and show that it is independent of the AdS radius and satisfies 2π/√3<γ≤π√2, above the values for four-dimensional Schwarzschild and Reissner--Nordström black holes. Using a Markov chain Monte Carlo (MCMC) forecast based on noiseless mock data with illustrative fractional uncertainties of 5%, we find that the dimensionless AdS radius can be constrained with a relative uncertainty of $16−−19\%$, whereas the charge can be distinguished from zero only for the near-extremal fiducial model considered. Under these assumptions, the subring exponent provides a Gaussian separation of $3.4−−5.9σ$ from the four-dimensional Schwarzschild black hole.
ER -