The GR Kerr Light program simulates the path of light in the equatorial plane near a rotating black hole using the Kerr metric. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the gr_kerr_light.jar file will run the program if Java is installed. The default setting is light with an initial r value of 3.0 near a black-hole with angular momentum parameter, J/M = 0.75.
Quelle: Open Source Physics