GRorbits is a general purpose interactive JAVA program that plots orbits of test particles and light flashes in the equatorial plane of a non-spinning (Schwarzschild) or a spinning (Kerr, with user-selected spin value) black hole. The software displays either the time-development of an orbit or the entire orbit over extended time. In the latter case the orbit changes instantly and continuously as the operator varies initial conditions. For the spinning Kerr black hole, the display shows the ergosphere (in which no particle can remain at rest) as well as the outer horizon and inner (Cauchy) horizon. The operator can use alternative global coordinate systems appropriate to the given black hole: Schwarzschild, Boyer-Lindquist, Gullstrand-Panlevé, and Doran. The interactive time-dependent display complements the static, analytic presentation of textbooks.

GRorbits is based on software developed by Adam Riess in a 1992 senior thesis at the Massachusetts Institute of Technology under Edwin F. Taylor. In 2011 Adam Riess was one of three awarded the Nobel Prize in Physics for work on the accelerating expansion of the Universe.

The GRorbits program is intended for use by anyone exploring general relativity. However, the program was developed specifically to coordinate with the proposed second edition of the text Exploring Black Holes: Introduction to General Relativity by Edwin F. Taylor, John Archibald Wheeler, and Edmund Bertschinger. (First edition 2000, Addison Wesley Publishers, ISBN 0-201-38423-X.)

The program is published under the GNU GPL licence. Its source code can be obtained using the email address bellow.

Programmed by Slavomir Tuleja