Answer: hydrostatic equilibrium ( inward pressure cancels out the outward pressure)
Explanation: Within the sun's core there is an outward force created by pressure while an inward force is been created from the surface by gravity. When this forces cancels each other out i.e outward force due to pressure equals inward force due to gravity; this is called hydrostatic equilibrium, this equilibrium is what keeps the sun in one piece, it is always stable and self regulating.
This is how the sun manages to stay stable and in one piece in spite of what happens at its core (hydrogen fuses to create helium)