Shadows and thin accretion disk images of the $\gamma$-metric

Understand

The $\gamma$-metric is a static, axially-symmetric singular solution of the vacuum Einstein's equations without an event horizon.

• This is a two-parameter family of solutions, generic values of one of which (called $\gamma$) measure the deviation from spherical symmetry.
• Here, we first study the shadow cast by this geometry, in order to constrain the $\gamma$-metric from observations.
• We find that for $\gamma < 1/2$, there are, in principle, no shadows cast.