How does the pressure supporting a main-sequence star like the Sun differ from that supporting a white dwarf?
Answer
The Sun balances gravity with thermal gas pressure from fusion; the white dwarf balances gravity with electron degeneracy pressure.
Active stars maintain hydrostatic equilibrium using the outward push of thermal pressure generated by fusion. White dwarfs have ceased fusion and are supported by the quantum mechanical resistance of tightly packed electrons.

Related Questions
What type of pressure primarily supports a white dwarf against gravitational collapse?What is the approximate maximum mass a white dwarf can have before collapsing catastrophically?What chemical elements predominantly constitute the inert core of a white dwarf formed from a star like our Sun?Why does a white dwarf's degeneracy pressure not drive the core hot enough to restart fusion?What is the ultimate, cold, dark fate of a white dwarf that continues to radiate away its stored energy?What is the primary source of energy that makes a white dwarf luminous when first formed?What type of event occurs if a white dwarf accretes enough mass to exceed the Chandrasekhar limit?How does the pressure supporting a main-sequence star like the Sun differ from that supporting a white dwarf?What happens to carbon and oxygen during a Type Ia supernova explosion?Why have black dwarfs not yet been observed in the universe?