These are the visual output of a gravity simulation program I wrote in C.
The basic setup in these are two large bodies orbiting around each other, with a third smaller body which flies around among them until it escapes the system or a certain amount of time has passed.
The color of the pixel corresponding to the starting point of the small body is determined by how long it lasted in the system. White means it escaped very soon and black means it lasted a long time.
I've been playing with this since around 1990 and eventually will do some more because I want to make more movies.
In 1990, making a movie was pretty much just a dream, but in 1999 when I could calculate at least 1 pixel per second (means a 640x480 image takes 80 hours to generate) I made one 365Kbyte movie which can be sen at http://chaosfugue.org/swirl/d16c.mpg
The movie is pretty rough, there aren't enough frames, and so sections are jumpy. Eventually will make a good smooth long version.