Null geodesic integration

Null geodesics describe in General Relativity the space-time trajectory of massless particles (e.g. photons). Numerically integrating the equations of motions describing the dynamics of these particles allows performing ray-tracing, i.e. to reconstruct the paths that light-rays would follow on a curved space-time around a massive object. In this tutorial we will examine the procedure in PyGRO to perform this operation and obtain the numerically integrated trajectory of a photon (or a bunch of them) in spacetime.