White Dwarfs

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A white dwarf is the burned-out core of a collapsed star that, like a dying ember, slowly cools and fades away (marked with circles in this image). However, the universe is not yet old enough for any white dwarfs to have cooled off completely to become invisible black dwarfs. White dwarf temperatures can therefore be used as "cosmic clocks" for estimating the age of the universe independently from other techniques.