Everything is working fine, but I want the objects to pass through each other without any collision and to keep an harmonic motion,. To see what I mean, try placing two planets on this simulation with 'Merge off'.
However, on my implementation, there's a point in which the bodies are very close and they make a huge force on each other, getting them into unexpected places.
I guess this can be solved by using adaptative time steps and/or trying different integration approaches. However, I'm sure there has to be a simple, hacky way to get the harmonic behaviour descrived above.