Photons shells inner structure and causal properties

Abstract

We shed light on some causal properties of the Kerr super-spinnars emerging through the investigation of the spacetimes photon shells. We define inner structure of the spacetime photon shell, constituted by regions distinguished by specific characteristics of the photons paths. These regions are reflected in the singularity shadow boundaries studied, in particular, in relation to repulsive gravity effects, known in a specific class of slowly spinning super-spinnars. Counter–rotating and co–rotating photons are particularly investigated. Super fast spinning solutions are characterized by “faint” shadow boundaries. The properties emerging from this analysis could be observed from specific regions of the spacetimes photon spheres boundaries. Slowly spinning super-spinnars, with (dimensionless) spin $1<a\le 1.17996$, are characterized by an articulated photon shell inner structure, evidenced close to the singularity rotational axis. This structure is analyzed for all view angles.