Although they are tiny in size, white dwarfs have played a great role in astronomy. These compact stars are very different from familiar objects like our sun. They also pose a seemingly endless series of puzzles, whose solutions provide new insights into many areas of physics and astronomy. To unravel a wide variety of phenomena such as cataclysmic variables (novae, dwarf novae), planetary nebulae, and some types of supernova, we have to understand white dwarfs. …showed first 75 words of 2617 total…

…showed last 75 words of 2617 total…of evolution for stars all along the "cooling track" and comparing these observations with theory, we can calibrate our models of white dwarf cooling. Then we can compare the number of observed cool white dwarfs with the theoretical predictions to give us an absolute determination of the time of the first epoch of star formation. White dwarfs will thus enable us to read the history of the Milky Way as frozen in its oldest stars.