Extreme gravitational lensing by supermassive black holes

TL;DR

This paper reviews recent advances in understanding extreme gravitational lensing caused by supermassive black holes, emphasizing analytical descriptions and future observational prospects.

Contribution

It provides a comprehensive review of the analytical modeling of strong gravitational lensing near black holes and discusses future detection requirements.

Findings

Complete analytical description of strong deflection limit

Discussion of future observational facilities

Review of recent progress in extreme lensing phenomenology

Abstract

Extreme gravitational lensing refers to the bending of photon trajectories that pass very close to supermassive black holes and that cannot be described in the conventional weak deflection limit. A complete analytical description of the whole expected phenomenology has been achieved in the recent years using the strong deflection limit. These progresses and possible directions for new investigations are reviewed in this paper at a basic level. We also discuss the requirements for future facilities aimed at detecting higher order gravitational lensing images generated by the supermassive black hole in the Galactic center.