White Dwarfs
A white dwarf is a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size.
White dwarfs are among the oldest objects in the galaxy and are the remnants of the earliest phases of star formation.
Typically, a white dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to the Sun's.
A typical white dwarf is slightly bigger than the Earth.
A white dwarf is one of the densest forms of matter (a density about 1 million times that of water!)
When white dwarfs are born they have a temperature greater than 100,000K.
A white dwarf cools down over the course of the next billion years.
Observing white dwarfs allows us to address a number of problems concerning the latter stages of stellar evolution.
As white dwarfs cool, from time-to-time they become unstable and begin to "ring", rather like an enormous church bell.
If we measure the ringing very accurately, we can tell how massive the star is, what it is made of and how fast it is cooling.