Strong Gravitational Lensing by Sgr A*

TL;DR

This paper reviews the potential of using extreme gravitational lensing near Sgr A* to test general relativity, focusing on the effects of a Reissner-Nordstrom-like term on relativistic images.

Contribution

It extends previous analyses of lensing by S stars by investigating how a Reissner-Nordstrom-like term influences relativistic images.

Findings

Large bending angles possible near black hole

Reissner-Nordstrom-like term affects relativistic image properties

Potential to probe black hole metrics through lensing observations

Abstract

In recent years, there has been increasing recognition of the potential of the galactic center as a probe of general relativity in the strong field. There is almost certainly a black hole at Sgr A* in the galactic center, and this would allow us the opportunity to probe dynamics near the exterior of the black hole. In the last decade, there has been research into extreme gravitational lensing in the galactic center. Unlike in most applications of gravitational lensing, where the bending angle is of the order of several arc seconds, very large bending angles are possible for light that closely approaches a black hole. Photons may even loop multiple times around a black hole before reaching the observer. There have been many proposals to use light's close approach to the black hole as a probe of the black hole metric. Of particular interest is the property of light lensed by the S stars orbiting in the galactic center. This paper will review some of the attempts made to study extreme lensing as well as extend the analysis of lensing by S stars. In particular, we are interested in the effect of a Reissner-Nordstrom like 1/r^2 term in the metric and how this would affect the properties of relativistic images.