Observational Appearance of a Freely-falling Star in an Asymmetric Thin-shell Wormhole

TL;DR

This paper investigates how a star's light appears to distant observers when falling into an asymmetric wormhole with two photon spheres, revealing unique luminosity decay patterns and flashes that could distinguish wormholes from black holes.

Contribution

It introduces the observational signatures of a star in an asymmetric wormhole, highlighting differences from black hole behavior due to the absence of an event horizon.

Findings

Luminosity decays or remains constant over time for wormholes.

Observers detect late-time light flashes against a bright background.

Distinct observational features can differentiate wormholes from black holes.

Abstract

It has been recently reported that, at late times, the total luminosity of a star freely falling in black holes decays exponentially with time, and one or two series of flashes with decreasing intensity are seen by a specific observer, depending on the number of photon spheres. In this paper, we examine observational appearances of an infalling star in a reflection-asymmetric wormhole, which has two photon spheres, one on each side of the wormhole. We find that the late-time total luminosity measured by distant observers gradually decays with time or remains roughly constant due to the absence of the event horizon. Moreover, a specific observer would detect a couple of light flashes in a bright background at late times. These observations would offer a new tool to distinguish wormholes from black holes, even those with multiple photon spheres.