WHITE DWARFS
The surprisingly extreme fate of an ordinary star like the Sun
A white dwarf represents the final stage in the evolution of a star like the Sun, following on from the comparatively brief red giant phase. During the previous phase, the core of the star was gradually shrinking and getting hotter while the outer layers expanded to enormous proportions. Eventually the core generates so much energy that it blows the outer layers off completely, leaving just the dense hot core behind. This core is the white dwarf, which will continue to exist, gradually losing its accumulated heat, for many billions of years. Although a white dwarf is extremely dense by ordinary standards, it’s not as dense as a neutron star, where all the matter has been compressed down to neutrons. While a neutron star packs all of a star’s mass into a volume just a few miles across, a white dwarf is around the same size as Earth. It’s still composed of atomic nuclei and electrons like ordinary matter, but squashed down to the point where the separation between electrons is comparable to their wavelength. This produces a phenomenon called degeneracy pressure which supports the white dwarf against any further collapse.