Multiple shadows from distorted static black holes

TL;DR

This paper investigates how external gravitational fields, specifically quadrupole distortions, affect the shadow of a Schwarzschild black hole, revealing conditions for multiple shadow images to form due to external matter influences.

Contribution

It introduces a detailed analysis of how quadrupole distortions cause multiple black hole shadows and derives conditions for their formation based on external gravitational parameters.

Findings

External matter sources modify the black hole's light ring structure.

Negative quadrupole moments lead to multiple shadow images.

A specific condition involving quadrupole moment and observer position determines shadow multiplicity.

Abstract

We study the local shadow of the Schwarzschild black hole with a quadrupole distortion and the influence of the external gravitational field on the photon dynamics. The external matter sources modify the light ring structure and lead to the appearance of multiple shadow images. In the case of negative quadrupole moments we identify the most prominent mechanism causing multiple shadow formation. Furthermore, we obtain a condition under which this mechanism can be realized. This condition depends on the quadrupole moment, but also on the position of the observer and the celestial sphere.