Stars usually form through gravitational collapse of gas clouds, not through the kind of bottom up process you are talking about. The physical phenomenon is cal

Stars usually form through gravitational collapse of gas clouds, not through the kind of bottom up process you are talking about. The physical phenomenon is called the Jeans instability and it only works for gas clouds above a certain density and temperature: https://en.m.wikipedia.org/wiki/Jeans_instability https://en.m.wikipedia.org/wiki/Jeans_instability Smaller things like moons and planets do form in the way you are talking about. There seems to be some limit on how big things can get if they are made this way, and typically we don't think you can get to the point where nuclear fusion starts.