Answer:
white dwarfs are hot, black dwarfs are cold
Step-by-step explanation:
a white dwarf is a slowly burning and aging corpse of a main sequence star such as our sun. they are up to 40 times hotter then the sun, ranking among one of the hottest objects in the universe, except their luminosity is so low that all their heat stays in them basically forever.
On the other hand, a black dwarf is a theoretical ending to a white dwarf, over the course of trillions of years, white dwarfs cool down into black dwarfs. black dwarfs rank among the coldest possible temperature. We aren't sure if these are really a thing, because we still haven't given white dwarfs enough time to cool down.