The first white dwarf star to be found was the companion to the bright star Sirius. Sirius and its companion are in mutual orbit about each other and this allows the mass of each to be found. White dwarfs are intrinsically very faint and are thus hard to detect. Despite this they are the end state for all medium mass stars and we thus expect that there are very many white dwarfs. The degenerate pressure in white dwarfs depends only on the star's mass and not on its temperature so that they are stable.
Some energy resides in the nuclear particles which are present together with the electrons.
The heat associated with the nuclear particles will gradually be radiated away and the stars will gradually cool over some billions of years. The presence of white dwarf stars in binary systems has been very important for the understanding of many violent outbursts in stellar systems. Supernovae of Type I, novae and cataclysmic variable stars are all cases where the companion to a white dwarf star has reached a point in its evolution where it is increasing in diameter and losing mass to the white dwarf. The deposition of material into an accretion disk about the white dwarf or on to the white dwarf's surface will determine the nature of any outburst. Bessell attributed this to the presence of a companion star but no companion was seen until Alvan Clark, while testing a new telescope saw a faint companion star.