Once formed, white dwarfs simply cool like hot stones lifted from a fire. Using our current understanding of the physics at high densities we can calculate the rate at which this cooling proceeds. Thus if we can measure the temperature of awhite dwarf we can estimate how long it has been cooling for and use it as a "cosmic clock" to place limits on the ages of star clusters, the Galactic disk and the Universe. To improve on these age estimates it is essential to continue developingour understanding of the interior structure of white dwarfs and the chemical make-up of their atmospheres. The assumptions made about each have a significant bearing on, for example, the outcome of the cooling rate calculations. The work of the Leicester White Dwarf Group is focused on obtaining and providing analysis of the observational data which is required to meet these challenges.

Image: An image of the open cluster M44 (the "Beehive") from the Palomar Sky Survey. This well known association contains as many as 20 white dwarfs which allow astronomers to place limits on the cluster age, investigate the initial mass-final mass relation and the white dwarf mass-radius relationship.