Lifecycle of a Star

A white dwarf is what stars like our Sun become when they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, such a star expels most of its outer material (creating a planetary nebula), until only the hot core remains, which then settles down to become a very hot (T > 100,000K) young white dwarf. Since a white dwarf has no way to keep itself hot unless it is matter from a …

…of giant glowing shells around the remains of the star. Layer after layer is blown off in this way, until the core of the star is revealed. With no energy being generated inside it, there is nothing to stop it collapsing as far as possible, forming a 'white dwarf' roughly the size of the Earth. With most of the star's mass compressed into such a small sphere, one cubic centimeter would weigh several hundred kilograms!