Naoki Tsukamoto, Tomohiro Harada, Kohji Yajima
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 letter, 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 the galactic centers because the radius of the relativistic Einstein rings for a wormhole lensing can be observed with the most powerful modern instruments, e.g. the Very Large Telescope Interferometer (VLTI), which have the resolution of $10^{-3}$ arcsecond. We may test some hypotheses of astrophysical wormholes by using the Einstein ring and relativistic Einstein rings in the future.
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http://arxiv.org/abs/1207.0047
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