White dwarfs

When a star with a mass similar to that of the Sun exhausts its store of nuclear energy, it can only release more energy by contracting. This will result in a star of enormous density. These objects are the extremely compact white dwarfs stars. Gradually a white dwarf cools down and after a few hundered million years it has a luminosity about 1 percent of the Sun's.

Eventually a white dwarf will cease to shine at all and it will become a black dwarf - a cold mass of degenerate gas floating through space. We have not yet observed a black dwarf and it may be that the Galaxy is not old enough for any star to have had time to become a black dwarf.

Recurring Nova T Pyxidis

If a white dwarf is orbiting around another star, a novae outburst can occur if they are close enough for material to get transfered from its companion. This novae is seen as an outburst of light. A novae is only bright for a few days or weeks and then it gradually fades away. After the outburst, the white dwarf reverts to its previous state but eventually the process is repeated.

Last modified 9th August 1999
Sarah Amandusson