Novel shadows from the asymmetric thin-shell wormhole

TL;DR

This paper reveals that asymmetric thin-shell wormholes can produce unique shadows that differ from black holes, depending on the photon sphere and spacetime asymmetry, offering potential observational signatures for wormholes.

Contribution

It introduces a novel shadow formation mechanism for asymmetric wormholes, showing shadows depend on spacetime asymmetry and differ from black hole shadows, with implications for future observations.

Findings

Wormhole shadows can be smaller than black hole shadows.

Discontinuous impact parameters lead to novel shadow features.

Differences in shadow sizes could help identify wormholes observationally.

Abstract

For dark compact objects such as black holes or wormholes, the shadow size has long been thought to be determined by the unstable photon sphere (region). However, by considering the asymmetric thin-shell wormhole (ATSW) model, we find that the impact parameter of the null geodesics is discontinuous through the wormhole in general and hence we identify novel shadows whose sizes are dependent of the photon sphere in the other side of the spacetime. The novel shadows appear in three cases: (A2) The observer's spacetime contains a photon sphere and the mass parameter is smaller than that of the opposite side; (B1, B2) there' s no photon sphere no matter which mass parameter is bigger. In particular, comparing with the black hole, the wormhole shadow size is always smaller and their difference is significant in most cases, which provides a potential way to observe wormholes directly through Event Horizon Telescope with better detection capability in the future.