A white dwarf is what stars become after they have used up their fuel. Near the end of its burning stage, this type of star releases most of its outer material, creating a planetary nebula. A nebula is leftover material from an old star. This is the place where new stars form! Only the hot core of the star remains. This core becomes a very hot white dwarf, with a temperature over 200,000°F! White dwarf stars are very dense because there is a lot of matter packed into a very small space!