Because white dwarfs are extremely small , it takes them a long time to cool down . Eventually , all white dwarfs will cool down into what is called a black dwarf .
Most observed white dwarfs have relatively high surface temperatures , between 8,000 K and 40,000 K. A white dwarf , though , spends more of its lifetime at cooler temperatures than at hotter temperatures , so we should expect that there are more cool white dwarfs than hot white dwarfs .