I'd posted the following on physicsforums but this is probably a better place (found this after listening to some astronomy cast episodes which are awesome).
I was reading the wiki page on dark matter, and have trouble visualizing how galaxies keep their shape if most of the stars rotate at the same rate. If I try to imagine this (ie: without any sort of math modelling of the gravity interactions involved) I picture everything just merging into a big amorphous disk instead of shapes like spirals.
Does anybody know of a nice animation or visualization of long term effects of a gravity model of a spiral galaxy? Ideally I'd like to see how the rotation would look over time with and without the dark matter distribution.