How does a white dwarf die?

A white dwarf dies when it can no longer sustain nuclear fusion and cools down to a low temperature over billions of years. Eventually, it may shed its remaining outer layers, leading to the formation of a planetary nebula, while the core becomes a cold, inert stellar remnant known as a black dwarf. However, the universe is not old enough for any black dwarfs to exist yet, as this process takes longer than the current age of the universe.