Shadows of rotating traversable wormholes surrounded by plasma

TL;DR

This paper investigates how plasma environments affect the observable shadows of rotating traversable wormholes, revealing potential signatures that distinguish them from black holes through size and formation of forbidden regions.

Contribution

It provides analytical expressions for wormhole shadows in plasma, explores plasma-induced forbidden regions, and identifies observational signatures differentiating wormholes from black holes.

Findings

Plasma profiles with radial dependence produce universal photon region evolution.

Angular-dependent plasma profiles lead to spacetime-specific photon regions.

Wormholes have lower critical plasma frequencies for shadow disappearance than black holes.

Abstract

We study the influence of the plasma environment on the shadows of stationary axisymmetric wormholes. We consider a sample of several wormhole solutions and plasma distributions for which the Hamilton-Jacobi equation for the light rays is separable. This allows us to derive analytical expressions for the shadow boundary and examine the behavior of the photon regions as the plasma frequency varies. We observe that plasma profiles which depend only on radial coordinate lead to common evolution of the photon region which does not depend on the wormhole metric and is consistent with the Kerr black hole. For plasma profiles with angular dependence the evolution of the photon region is specific for every spacetime thus wormholes are observationally distinguishable. We further investigate the formation of forbidden regions in the plasma medium where light cannot propagate. They lead to the formation of plasma frequency ranges where the shadow is no longer observable and we show that this phenomenon is characteristic for all the configurations in our sample. We obtain the critical frequencies for which the shadow vanishes and demonstrate that for all the wormholes they are lower than the critical frequencies for the Kerr black hole in the same environment. This implies that there exist plasma frequency ranges in which the Kerr black hole casts a shadow but wormholes do not, creating a strong observational signature for discriminating between compact objects. In the frequency ranges where both black hole and wormhole shadows exist the wormhole shadows are consistently smaller than those for the Kerr black hole. As the plasma frequency grows the discrepancy progresses showing that plasma medium facilitates the experimental detection of wormholes. Finally we consider aberrational effects on the wormhole shadows. They further increase the deviation from black holes making wormholes easier to detect.