Can we distinguish between black holes and wormholes by their Einstein-ring systems?

TL;DR

This paper investigates whether Einstein-ring systems can differentiate black holes from wormholes, proposing observational methods to distinguish them based on ring radii and current telescope capabilities.

Contribution

It demonstrates that Einstein rings and relativistic Einstein rings can, in principle, be used to distinguish black holes from wormholes through their radii and observational signatures.

Findings

Relativistic Einstein rings by wormholes are detectable with current technology.

Black holes produce smaller relativistic Einstein rings, currently unmeasurable.

Potential to test astrophysical wormhole hypotheses using Einstein-ring observations.

Abstract

For the last decade, the gravitational lensing in the strong gravitational field has been studied eagerly. It is well known that, for the lensing by a black hole, infinite number of Einstein rings are formed by the light rays which wind around the black hole nearly on the photon sphere, which are called relativistic Einstein rings. This is also the case for the lensing by a wormhole. In this paper, we study the Einstein ring and relativistic Einstein rings for the Schwarzschild black hole and the Ellis wormhole, the latter of which is an example of traversable wormholes of the Morris-Thorne class. Given the configuration of the gravitational lensing and the radii of the Einstein ring and relativistic Einstein rings, we can distinguish between a black hole and a wormhole in principle. We conclude that we can detect the relativistic Einstein rings by wormholes which have the radii of the throat $a\simeq 0.5$pc at a galactic center with the distance 10Mpc and which have $a\simeq 10$AU in our galaxy using by the most powerful modern instruments which have the resolution of $10^{-2}$arcsecond such as a 10-meter optical-infrared telescope. The black holes which make the Einstein rings of the same size as the ones by the wormholes are galactic supermassive black holes and the relativistic Einstein rings by the black holes are too small to measure at this moment. We may test some hypotheses of astrophysical wormholes by using the Einstein ring and relativistic Einstein rings in the future.