A white dwarf is what stars like the Sun become after they have beat their nuclear fuel. At the end of its nuclear burning stage, this type of star casts out most of its outer material creating a planetary nebula. Only the hot core of the star remains. The core becomes a very hot white dwarf with a temperature excelling 100,000 Kelvin. Unless it is accreting matter from near star, the white dwarf cools down over the next billion years or so. Many nearby young white dwarfs have been exposed as sources of soft or low energy x-rays. Soft x-ray and extreme ultraviolet observations have become a powerful tool in the study composition and structure of the thin atmosphere of these stars.