Black hole mimicker hiding in the shadow: Optical properties of the $\gamma$-metric

Understand

Can the observation of the "shadow" allow us to distinguish a black hole from a more exotic compact object? We study the motion of photons in a class of vacuum static axially-symmetric space-times that is continuously linked to the Schwarzschild metric through the value of one parameter that can be interpreted as a measure of the deformation of the source.

• We investigate the lensing effect and shadow produced by the source with the aim of comparing the expected image with the shadow of a Schwarzschild black hole.
• In the context of astrophysical black holes we found that it may not be possible to distinguish an exotic source with small deformation parameter from a black hole.
• However, as the deformation increases noticeable effects arise.