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 variable-spin (Kerr) 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.
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 latest versions of GRorbits may be downloaded from http://www.eftaylor.com/grsoftware/.
Basic instructions for manipulating each of the three panels of the display appear at the bottom in red when the cursor is placed in that panel.
The diagram below shows how to make small changes in orbit parameters.
Definition of terms describing the black hole and orbit parameters can be found in the Index of Exploring Black Holes or in the Glossaries of Symbols and Terms near the end of that volume.
At the bottom left of the display are the numerical values of two times. The first time, called t, is either the bookkeeper time or the so-called rain time, depending on the selection by the operator under the Program Mode menu. The second time is tau (), the proper or wristwatch time of the orbiter. The proper time for and orbiting light flash is always zero. (Unfortunately, on some platforms the symbol tau looks like a capital T.)
You may obtain email help from either
Slavo Tuleja: stuleja@gmail.com
or
Edwin Taylor: eftaylor@mit.edu
There is no such thing as a free lunch; you will be asked for your reactions to the program and for suggestions to improve it.
© Slavomir Tuleja (2007)