White dwarfs are the final remnants of low and intermediate mass main sequence stars. Because of electron degeneracy, their evolution is just a cooling process. The basic ingredients to understand their evolution are well identified (although not all of them completely understood), and there is at present an important observational background that allows to check the different models of cooling.
The majority of white dwarfs can be imagined as a degenerate core made of a mixture of 12C, 16O plus several impurities that contains the bulk of mass and acts as an energy reservoir, surrounded by a semidegenerate envelope that controls the flux of energy from the interior to free space. Since the corresponding cooling rate can be obtained from their luminosity function or the secular drift of their period of pulsation, it is possible to consider them as a calorimeter turning around the center of the Galaxy. Therefore, these properties can be used to detect the existence of additional, unexpected, energy sources or sinks. In this talk I describe how white dwarfs can be used as detectors and I apply them to the case of axions.