What happens to bodies of mass as they approach and get near this value? If they don't actually reach the criteria, will their properties be vastly different from bodies that do reach the criteria? Will it expand instead of maintain it's radius? I'm also wondering how much energy it takes to compress a body down to this radius. I would imagine that at some point during the compression, the body loses all of it's material properties and needs to be treated more like a soup of atoms, so the actual material used doesn't really matter.