You also can not get a fusion reaction from iron. Iron is the end of the line, formation of elements beyond iron (increasing atomic number) is endothermic. The hierarchy is sort of hydrogen, helium, carbon, silicon, then finally iron.
It must be all this recent dark matter business that is bringing this gravitational theory stuff back up.
I do know one thing, and that is that we seem to know enough about gravity to be dangerous, and that is about all.