Double shadows of reflection-asymmetric wormholes supported by positive energy thin-shells

Abstract

We consider reflection-asymmetric thin-shell wormholes within Palatini f(R) gravity using a matching procedure of two patches of electrovacuum space-times at a hypersurface (the shell) via suitable junction conditions. The conditions for having (linearly) stable wormholes supported by positive-energy matter sources are determined. We also identify some subsets of parameters able to locate the shell radius above the event horizon (when present) but below the photon sphere (on both sides). We illustrate with an specific example that such two photon spheres allow an observer on one of the sides of the wormhole to see another (circular) shadow in addition to the one generated by its own photon sphere, which is due to the photons passing above the maximum of the effective potential on its side and bouncing back across the throat due to a higher effective potential on the other side. We finally comment on the capability of these double shadows to seek for traces of new gravitational physics beyond that described by General Relativity.

Light ring images of double photon spheres in black hole and wormhole space-times

“…Among them, and focusing on spherically symmetric geometries 2 , we find the presence of two critical curves, since they might induce additional concentric light rings around the central brightness depression [54]. Such double critical curves may arise, for instance, in reflection-asymmetric wormhole solutions [55][56][57][58], or in models having an absolute maximum of the effective potential at the center [59,60]. The latter class of models admits different implementations like the one of the family of black bounce-type solutions found in [61], whose strong deflection limit was recently discussed in [62].…”

Observational signature and additional photon rings of an asymmetric thin-shell wormhole

“…Then more examples of asymmetric thin-shell wormhole are studied in Refs. [39][40][41], of which the authors named their results as double shadows [39]. It is worth noting that double shadows should be called double critical curves or photon spheres in the context of our article.…”

Shadows and optical appearance of black bounces illuminated by a thin accretion disk

“…Finally, the presence of wormhole structures yields interesting new possibilities, such as shadows from objects without accretion disks due to contribution of those disks on the other side of the wormhole and flowing through the wormhole throat, or the generalization of our analysis to reflection-asymmetric wormholes since they produce effective potentials with two maxima (i.e. two unstable circular orbits), which can be capable to yield additional light rings [56,57].…”