As the first clouds of interstellar dust is forming the friction is slowly building up the heat.

X-Grav is a simple physics simulation for a large number of particles. It simulates the effect of gravity, collisions, heat dissipation and a simple chemical reaction. The simulation is in no way meant to be realistic but rather a toy with which you can create stars, planets and even simple solar systems.

The best way to understand the behaviour of X-grav is by a demonstration. Start by compiling xgrav and then start it by doing:

xgrav -s example1.g

This will start a simulation containing 2000 particles which are all cold from the begining. After a while these particles will have collapsed into a few clouds which are warmed up by the friction of the particles. When the temperature and density of these clouds have raised enough some of the colliding particles will ignite in a burst of fusion. This will lead to a chain reaction igniting a large number of the combustible particles, raising the temperature of the cloud so rapidly that the particles are blown appart from the increased pressure. Under most circumstances this sudden reaction will blow out the initial flames.

However if you wait a while and if the conditions are right you this will not happen the second or third time the particles form dense clouds again. The chain reaction will be a little calmer due to less combustible material and will rather live on. You will now have a small star which is fueled by continous reactions of colliding particles.

When the heat is high enough, the first chain reactions can start. Finally leading to the creation of a stable star.

If you let the simulation run for a while you will see that there are less and less material left in the stars which can react. As the stars are cooling down you can note that they are shrinking until they are cold and dark dwarfs.

As the first clouds of interstellar dust is forming the friction is slowly building up the heat.

During the simulation you can use the 'a' and 's' keys to zoom in and out of the center of the simulation. When you are satisfied with the demonstration you can use the escape key to quit the program.

Hopefully this small demonstration will have made you interested in the simulation. When we ran this simulation we only used 2000 interacting particles in order to get the results somewhat in real time. If you are a little more patient you can instead run xgrav with the 'record' and the 'play' settings. By doing 'xgrav -r foo.dat < example2.g' you instruct xgrav to save all the simulated particles continously in the datafile 'foo.dat'. After quiting xgrav you can later playback and resume the simulation with 'xgrav -p foo.dat'.

Last modified 03/13/12