Dynamical Friction 1

I made a first attempt to simulate one heavy particle falling into a "halo" of light particles. The procedure was the following: Using Walter's original initial conditions (which are similar but not identical to Binney's), I simulated forward well past the time when the object has virialized. I then dumped out the particle positions and velocities. From this file, I create a new initial condition file, adding one single particle some distance outside the edge of the virialized object. I then run the simulation forward again, for the same amount of time (i.e. long enough to hope that system can come to an equilibrium configuration). My inexperience shows here, I think I picked too high of a heavy particle mass... it was 1000 times more massive. The upshot is that the heavy particle more or less destroys the halo immediately, and it doesn't really re-form by the time the simulation ends.

I saw a great talk by A. MacFadyen, and it had a lot of really pretty movies. I was inspired to try it myself, it turned out to be fairly easy with Python. My movies are less pretty than his, so far. Here is a movie of the heavy particle falling in. The frames are in time intervals of 1 for 300 (in arbitrary time units). One interesting thing is that there is a little knot of the small particles that seems to be long lived, and orbits around the large guy for roughly the whole time.



Also, it's useful to look at the stills, so here are a few, at times (0,1,2,5) and then longterm at times (50,100,200,300). One thing I noticed is that the infalling particle seems to re-introduce some order into the phase space of the little guys that was definitely not there in the initially virialized object.


Also, Scott sent me a list of questions over e-mail. I'll start answering them as I get the answers. I'll send note about this post now, though.