What happens to white dwarfs as they age?

As white dwarfs age, they gradually cool and dim over time, losing their residual heat. They do not undergo further fusion reactions, so they slowly radiate away their energy. Eventually, they may become cold, dark remnants known as black dwarfs, although the universe is not old enough for any black dwarfs to currently exist. This process can take billions of years, leading to a slow transition from a hot, glowing state to a nearly invisible one.