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Circular orbits around regular black holes: Shadows as diagnostics of nonlinear electrodynamics
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DOI:10.1016/j.aop.2026.170625.png)
Abstract
En 中文
We investigated the properties of circular orbits in spherically symmetric, static, regular spacetimes arising from general relativity coupled with nonlinear electrodynamics. Focusing on Bardeen-like, Hayward-like, and Maxwellian families and comparing them with the singular Reissner–Nordström solution, we derived the parametric bounds separating black hole and no-horizon configurations. We showed that characteristic circular orbits for test particles shrink with an increase in charge parameter and persist even in the absence of an event horizon, up to a critical charge limit. A crucial distinction is made between standard null geodesics and the effective photonsphere governing light propagation in nonlinear electrodynamics. We found that while null geodesics in no-horizon geometries are restricted to specific values of charge parameters, the effective photonsphere exists for all values. Additionally, we demonstrated that the shadow radius can serve as a diagnostic for Lagrangian pathologies, evidenced by a discrepancy in Bardeen-like and Hayward-like models in the vanishing charge limit. Finally, we computed eikonal quasinormal modes to clarify the geodesic correspondence for perturbations.
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