I often hear that stars form when giant clouds of hydrogen start to collapse under gravitational forces, so I started thinking about this. Gravity depends on the masses and distances of objects. So how many atoms of hydrogen would you need, and at what average distance would the atoms need to be spaced in order for a cloud of hydrogen to start collapsing upon itself? The collapse begins to happen toward the center of mass of the cloud. At what point do you stop viewing the picture as a bunch of individual particles spread out over a space, and start viewing it as a single “object” with a center? I assume this would have something to do with the center of mass calculation? The mass of a hydrogen atom is so small that the gravitational attraction of two hydrogen atoms to one another is ridiculously small at any distance. How can such a small acceleration due to gravity, even with lots of atoms, result in such an avalanche of acceleration toward one center point?