The Sun does not expand or contract because it is in a state of

A. Galilean equilibrium. That is to say the sunspots Galileo observed dictate the Sun's static nature.

B. coronal equilibrium. That is to say the surface of the Sun does not exhibit coronal mass ejections.

C. hydrostatic equilibrium. That is to say the inward force of gravity is balance by the outward pressure from nuclear fusion.