 As a star 's core shrinks , the intensity of radiation from that surface increases , creating such radiation pressure on the outer shell of gas that it will push those layers away , forming a planetary nebula . If what remains after the outer atmosphere has been shed is less than 1 @.@ 4 M ☉ , it shrinks to a relatively tiny object about the size of Earth , known as a white dwarf . White dwarfs lack the mass for further gravitational compression to take place . The electron @-@ degenerate matter inside a white dwarf is no longer a plasma , even though stars are generally referred to as being spheres of plasma . Eventually , white dwarfs fade into black dwarfs over a very long period of time . 
