My PhD is centered around the general-relativistic radiative transfer code RAPTOR (short for RAdboud Polarized integraTOR). This code is capable of creating simulated observations of accreting black holes using the ray-tracing method. It is described in detail in the following two papers:

RAPTOR I: Time-dependent radiative transfer in arbitrary spacetimes

RAPTOR II: Polarized radiative transfer in curved spacetime

The code is also available on GitHub.

Video of an accreting black hole using RAPTOR. The accreting system is rotated to offer a view from different observer-inclination angles. The video uses data generated in HARM2D (Gammie et al., 2003).