How do astronomers use white dwarfs to estimate the age of structures like star clusters?

Answer

By observing the temperature of the hottest white dwarf present

The coolest white dwarfs have cooled for the entire age of the structure; by observing the temperature of the hottest remaining white dwarf, astronomers can calculate how long the cluster has existed based on known cooling times.

How do astronomers use white dwarfs to estimate the age of structures like star clusters?
starsstellar evolutionastrophysicswhite dwarfBlack Dwarf