What's your level of maths/physics? It could help everyone give you some pointers or references. For example, if I'd claim that a ball of homogenous, initially unmoving, dust roughly the size of Earth needs only a few minutes to gravitationally collapse into a single body, would you: - Be completely astounded and unable to prove or disprove this statement. - Obtain a rough approximation after looking up some integrals or some old classical mechanics book you have lying around. - Call my bluff and make it into a game of physics chicken. - Make an N-body simulation and go for a coffee while it computes. - Consider cases where matter pressure is and isn't equal to 0. Find the p = 0 as trivial. - Something completely different. It's not like I wasn't just guessing and being slightly facetious. ;)