Changes

White dwarfs range in mass from 0.17 to 1.33 solar masses with the majority between 0.5 and 0.7 solar masses.  Their volume though is roughly that of the Earth.  As such, a typical white dwarf has a density of 1x10³ kg/m³ which is around 200,000 times the density of the Earth or one million times the density of the Sun.

White dwarfs range in mass from 0.17 to 1.33 solar masses with the majority between 0.5 and 0.7 solar masses.  Their volume though is roughly that of the Earth.  As such, a typical white dwarf has a density of 1x10³ kg/m³ which is around 200,000 times the density of the Earth or one million times the density of the Sun.

This density is brought about by [[gravity]] crushing the [[electrons]] of [[atoms]] together.  Normally electrons with the same spin cannot occupy the same energy level, therefore only two electrons can occupy a single energy level (as electrons can spin only one of two ways).  Because in a white dwarf the electrons are forced so closely, all the energy levels of the atoms are filled with electrons, and because no more than two electrons can fill the energy levels in the atoms within the white dwarf, the star become [[degenerate]].  At this point, there is insufficient gravity to compress the matter any more, as [[quantum mechanics]] will not allow for it, preventing the white dwarf from collapsing any further, stabilizing it.<ref name="nasa">http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html</ref>

This density is brought about by [[gravity]] crushing the [[electrons]] of [[atoms]] together.  Normally electrons with the same spin cannot occupy the same energy level, therefore only two electrons can occupy a single energy level (as electrons can spin only one of two ways).  Because in a white dwarf the electrons are forced so closely, all the energy levels of the atoms are filled with electrons, and because no more than two electrons can fill the energy levels in the atoms within the white dwarf, the star becomes [[degenerate]].  At this point, there is insufficient gravity to compress the matter any more, as [[quantum mechanics]] will not allow for it, preventing the white dwarf from collapsing any further, stabilizing it.<ref name="nasa">http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html</ref>

Gravity at the surface of a white dwarf is around 100,000 times that of the Earth, the result is that heavier atoms in the atmosphere will sink into the surface, leaving only the lightest elements behind.  Thus the thin atmosphere is made up mainly of [[hydrogen]] and [[helium]].  The temperature at this surface can range from 40,000 to 8,000 K, although white dwarfs as cool as 3,900 K have been found.  The cooler the white dwarf, the older it is likely to be as they lose thermal energy over time.<ref>http://adsabs.harvard.edu/abs/2004ApJ...612L.129G</ref> The surface itself is composed of a crust of [[carbon]] and [[oxygen]], the bottom of which is believed be a crystalline lattice.<ref name="nasa">http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html</ref>

Gravity at the surface of a white dwarf is around 100,000 times that of the Earth, the result is that heavier atoms in the atmosphere will sink into the surface, leaving only the lightest elements behind.  Thus the thin atmosphere is made up mainly of [[hydrogen]] and [[helium]].  The temperature at this surface can range from 40,000 to 8,000 K, although white dwarfs as cool as 3,900 K have been found.  The cooler the white dwarf, the older it is likely to be as they lose thermal energy over time.<ref>http://adsabs.harvard.edu/abs/2004ApJ...612L.129G</ref> The surface itself is composed of a crust of [[carbon]] and [[oxygen]], the bottom of which is believed be a crystalline lattice.<ref name="nasa">http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html</ref>