White Dwarf

Remnant of a star with mass <8 Msun. White dwarfs have masses <1.4 Msun (the Chandrasekhar mass) and are supported by electron degeneracy pressure. White dwarfs have radii ~Rearth (<0.02 Rsun) and densities ~105-6 g/cm3. No
nuclear fusion or gravitational contraction occurs in white dwarfs, they shine by residual heat. The surface has a very high temperature and radiates mainly in
the ultraviolet. White dwarf varieties are defined by the elements that dominate their surfaces as revealed by their spectra. However, if material is accreting onto the surface of a white dwarf from a companion star, the spectral will reflect this fact. Nearly all white dwarfs have C-O cores. Three varieties (DA, DB and DO) have
nearly pure surfaces of either H or He; PG 1159 stars appear to have partially exposed cores. White dwarfs with mixtures of elements on their surfaces receive
compound classifications. For example, DAB stars contain H and He, whereas DAO stars have H and ionized He.


Image source: http://www.daviddarling.info/encyclopedia/W/whitedwarf.html.