Interplay of gravity and nuclear fusion. Electrons prevent further collapse. Size about that of Earth. Outer layers are planetary nebula. Supernova happens when neutron star is created.
Neutrons prevent further collapse.
Size about that of a large city. Highest mass core shrinks to a point. On the way to total collapse it may momentarily create a neutron star and the resulting supernova rebound explosion. Gravity finally wins. Nothing holds it up.