GalaxyMerger is a program for modelling the gravitational interaction of galaxies. The primary goal was to overcome the annoying O(n²) growth in calculation time when using a traditional force calculation apporach. The program is therefore based on the Barnes-Hut algorithm which has a growth of O(n log n) (depending on implementation). This algorithm was first presented in "A Hierachical O(n log n) Force Calculation Algorithm" by J. Barnes and P. Hut, Nature, v. 324, December 1986.
To improve the speed of the algorithm I have implemented cell-cell force calculations, and thus gained a factor 2 in speed over the original Barnes-Hut. The simulation is visualized in a window shoving X-Y, X-Z and Y-Z planes simultaneously, and the interacting galaxies can be colored according to acceleration, velocity, type of particles, or the initial distribution of the particles.
The simulations initial conditions and progress can be saved and reloaded, and the program can save bitmaps at selected intervals. It can also generate a video of the entire simulation, using any encoder installed on your machine.

Click here to download the program. At this moment I've not made any helpfiles for this program, but if you know what you are dealing with (galaxies and such...) it should be straight forward.

Click here to view a video (DIVX) of a simulation with 400.000 particles. This simulation took 10 hrs on my dual Athlon XP 1800+.

Here is some frames from another simulation made with GalaxyMerger, also with 400k particles.
Red is dark matter (85% of the mass) and blue is the disc stars