From massless wormholes to massive black bounces: Shadows and multiple light rings

Abstract

We develop a general framework for constructing massive black bounce geometries from massless wormhole seeds by introducing a position-dependent mass function while preserving the underlying areal-radius profile. We apply this procedure to the generalized Ellis-Bronnikov wormhole and obtain a new family of generalized Bardeen-like black bounce space-times, which continuously interpolates between traversable wormholes and regular black holes. We investigate the motion of massive particles and photons and show that, in contrast with the simpler orbital structure of the massless generalized Ellis-Bronnikov geometry, the generalized Bardeen-like space-time can exhibit multiple circular orbits and a rich light ring structure, including configurations with two unstable circular photon orbits separated by a stable one. We determine the corresponding photon sphere and shadow radii and compare our predictions with Event Horizon Telescope observations of Sgr A*, deriving observational constraints on the parameter space of the model. We further investigate the optical appearance produced by a geometrically and optically thin accretion disk through ray tracing. Multiple light rings generate characteristic nested structures in the high-resolution intensity profiles, whose relative brightness is strongly affected by the mass deformation and gravitational redshift. However, after modeling the finite angular resolution of the EHT with a Gaussian beam convolution, these fine structures are largely washed out, revealing a strong observational degeneracy between these exotic compact objects and standard black hole geometries at current EHT resolution.