Astrophysical observables for regular black holes with sub-Planckian curvature*

We investigate the photon sphere and marginally stable circular orbit of massive particles over the recently proposed regular black holes with sub-Planckian curvature and a Minkowskian core. We derive the effective potential for geodesic orbits and determine the radius of circular photon orbits, with an analysis of the stability of these orbits. We extend our analysis to the background of a compact massive object (CMO) without a horizon, whose mass is below the lowest bound for the formation of a black hole. For massive particles, marginally stable circular orbits become double-valued in the CMO phase. Through a comparison with Bardeen and Hayward black holes, we also find that the locations of the photon sphere and marginally stable circular orbit in the CMO phase with a Minkowskian core are evidently different from those in the CMO phase with a dS core, which potentially provides a way to distinguish between these two types of black holes by astronomical observation. Finally, we present the observational constraint on the deviation parameter for such regular black holes using observed data from the black hole M87*.

Automated summary

We investigate the photon sphere and marginally stable circular orbit of regular black holes with sub-Planckian curvature and a Minkowskian core. The stability and location of these orbits are analyzed, and a comparison with other black holes is made. We also discuss the potential of distinguishing between different types of black holes through astronomical observations. Furthermore, we present observational constraints on the deviation parameter for such regular black holes using observed data from the black hole M87*.