The pressure balancing gravity in a star like the sun comes from electromagnetism. Neutron stars are so heavy that the pressure comes from the nuclear forces an

The pressure balancing gravity in a star like the sun comes from electromagnetism. Neutron stars are so heavy that the pressure comes from the nuclear forces and degeneracy pressure (the same reason there are at most two electrons per orbital in chemistry). They are really fundamentally different objects. A neutron star is more like an enormous nucleus bound by gravity, while the sun is just plasma with an occasional nuclear reaction happening. Future changes in the sun's radius have more to do with its changing composition over time, which alters the reactions that can occur and their rates, which subsequently change the balance between pressure and gravity. https://en.m.wikipedia.org/wiki/Main_sequence https://en.m.wikipedia.org/wiki/Main_sequence