Multi-photon ring structure of reflection-asymmetric traversable thin-shell wormholes

TL;DR

This paper investigates the optical signatures of reflection-asymmetric traversable thin-shell wormholes in Palatini $f(R)$ gravity, revealing unique multi-photon ring structures and shadow features that could distinguish them from black holes in high-resolution imaging.

Contribution

It introduces a novel simulation of accretion disk images around asymmetric wormholes, highlighting distinctive multi-ring structures caused by light crossing the throat, different from black hole shadows.

Findings

Multiple photon rings due to light crossing the throat

Significant reduction in shadow size compared to black holes

Enhanced luminosity and number of rings in two-disk scenarios

Abstract

We consider the observational signatures of thin accretion disks around a reflection-asymmetric traversable thin-shell wormhole. This wormhole, built in the framework of Palatini $f(R)$ gravity coupled to a Maxwell field using a junction conditions formalism, lacks horizons but features photon spheres on each side of the throat, described by different effective potentials and at different locations. This fact allows a portion of the light rays arriving to the observer's screen on one side of the throat to have explored a part of the space-time on the other side, bringing information about the geometry gathered there. In this setting we simulate the optical appearance of such an asymmetric wormhole when illuminated by thin accretion disks, investigating scenarios with either one or two (on each side of the throat) disks, revealing a rich multi-photon ring structure due to light crossing the throat, and a strong reduction in the size of the central brightness depression region. These new rings are more numerous and far more luminous in the two-disk case than in the single-disk case, and the shadow's size reduction far more acute, making a neat distinction as compared to canonical black hole images. These results highlight the potential of high-resolution imaging in providing smoking guns for the existence of ultra-compact objects distinct from black holes via their multi-ring structure.