Today, one of my friends and I got into a conversation based on astronomy. Our conversation eventually led to galaxies and there is one question he brought up that I just can't seem to answer. The question is "Why are galaxies disc shaped?" We found out that this does not only apply to galaxies, but solar systems as well. When solar systems are only in their infancy, the dust that is left over from the formation of the star gathers into a disc as well. This eventually leads to the formation of the planets. Also, rings that form around a planet are very thin and in a near perfect disc shape. It seems like the only way to get a "sphere" of multiple objects (such as an Elliptical Galaxy) is with some sort of gravitational disturbance. So my question is to you guys, how do orbits of multiple objects usually end up to create a disc and not a sphere or some thing related to a sphere?