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White Dwarf stars
A white dwarf star is an extremely dense stellar remnant (or "compact star"). Typical white dwarfs have mass approximately equal to that of the sun but radius approximately equal to that of the earth. A star shrinks to a white dwarf when it stops undergoing nuclear fusion. If it is a member of a multiple star system, it might start acquiring matter from a neighboring star (which in turn may lead to the ignition of carbon fusion, which almost immediately leads to a supernova). White dwarfs don't undergo nuclear fusion, so they have no energy source; nor does the heat from former fusion support it against gravitational collapse. The only thing keeping it together is pressure from "electron degeneracy".