Question

How is it possible for white dwarfs to have a lower luminosity than the sun even though it is much cooler?

Answer 1

Answer:

White dwarfs have an extremely small surface area to radiate this heat from, so they cool gradually, remaining hot for a long time.

Explanation:

As a white dwarf cools, its surface temperature decreases, the radiation which it emits reddens, and its luminosity decreases.