The black hole photon ring with AART: an Adaptive Analytical Ray-Tracing code

Horizon-scale observations of astrophysical black holes have initiated another chapter of strong-field studies of general relativity. As technological advances continue to improve our observations, it will become necessary to compare the resulting data against increasingly detailed theoretical predictions. In this talk, I will introduce a numerical framework that exploits the integrability of the Kerr spacetime and solves the null geodesic equation by evaluating elliptic functions, instead of direct numerical integration of the geodesic equations. We implement an adaptive non-uniform resolution for each lensing band (defined as the region in the image in which rays orbit a given number of times before arriving at the detector) suitable for detailed studies of the black hole photon ring. We demonstrate its computational performance by presenting black hole high-resolution movies of non-stationary and non-axisymmetric source profiles around Kerr black holes that can be computed on personal computers in less than five minutes.