Modeling Diffusion in Accreting White Dwarf Stars : The Life of a Dead Star

Color poster with text, charts, and images.A white dwarf star is a very small, very dense star. They are usually about the size of the Earth, but have about the same mass as the Sun. A single teaspoon of material from a white dwarf may weigh more than a large dump truck. A white dwarf star is the heavy core of what was once a much larger star. At the end of its life, this larger star blew off all its outer layers and left behind only a carbon and oxygen core; this is the white dwarf. White dwarfs are not held together by the same forces that hold most starts together. They are held up by a quantum mechanical effect called electron degeneracy pressure. This is a much weaker force than the thermal pressure from nuclear fusion that holds up most stars and does not generate any new energy; the white dwarf just slowly burns the energy it had saved up as a larger star. One of the interesting effects of being held up by this degenerate matter is that more massive white dwarfs actually have smaller radii! Under normal conditions, a white dwarf will just slowly radiate away the energy that it had saved up while it was a main sequence star, eventually becoming a black dwarf. This happens over a longer period than the current age of the universe; no white dwarfs have become black yet. Under certain conditions however, a white dwarf may die in a spectacular explosion called a type Ia supernova.University of Wisconsin--Eau Claire Office of Research and Sponsored Program