Why? Because * people need to be educated, and this article does a good job * different forces dominate at different sizes For a skull, gravitational forces

Why? Because * people need to be educated, and this article does a good job * different forces dominate at different sizes For a skull, gravitational forces of a human head are tiny. Collapse is prevented because of skull rigid structure that supports itself: inward forces are resisted by resistance to deformation and pressure (similar to semi-spherical cellars and rounded bridges) Earth has large gravitational forces, but resistance to compresson of its solid inner core and liquid iron outer core prevents collapse. Stars are much bigger, and the larger gravitational forces are resisted by an additional force, next to resistance of compression gasses: Nuclear reactions produce radiation in the form of photons that are streaming out from the star's interior creating outward pressure forces.