A Star whose nuclear energy sources has been exhausted, except in the outermost layers. About 14% of all stars in our Milky Way Galaxy. Example: Sirius B, the binary companion of Sirius is a White Dwarf. Gravitational collapse causes the star to contract to a size of about 1/100th that of the Sun, with a density one million times that of the Sun. Only stars of less than l.25 solar masses become white dwarfs. Weak nuclear reactions and gravitational energy of contraction continue to keep the white dwarf dimly shining.