Did you know?
That White Dwarfs, in spite of their size, are one of the most dense forms of
mass in our discovered Universe? White dwarfs have a density of 1 x 109 kg/m3.
For reference, the density of earth is 5.4 x 103 kg/m3. That means that even a
tsp of matter from a white dwarf star would weigh multipe ton!
White dwarfs are are the last stage of the life cycle of an average sized, alternatively a small star with a mass between 0.3 - 8M (solar masses). When the mass of a white dwarf star increases, the size decreases as well as the radius. This is different compared to the average stars, which increases in size and radius when the mass increases. When the density of a star increases, gravity increases along with it. Shortly explained, added mass leads to increased gravity. This pressure does not increase much though, in fact it increases very little. This leads to the star shrinking in mass because of, again, gravity. One of the many differences between massive stars and white dwarfs is that a massive star eventually has to shed the majority of their mass as a planetary nebula. If not, the final contraction to a white dwarf, is incapable of being halted by the degenerate electrons. Unless the mass is capable of shedding and does so accordingly, the star will turn into a black hole or a neutron star.
White dwarfs start off as a stellar nebula, which is a large cloud
of dust and plasma as well as helium (He) and hydrogen (H).
This cloud pulls itself together and merges toward the center
because of gravity. The matter that gathers in the center of the
then causes the temperature to rise to such an extent that it
triggers a nuclear fusion.
With time, the white dwarf star cools down in temperature because
of the energy that is extended and radiated outwards. This happens
because when the white dwarf star contracts enough and reach their
final size, all the nuclear fuel to burn is used. This is called
radiative cooling. There is also a second method or process for
the cooling of white dwarf stars called neutrino cooling. This
process occurs when the star has a very high temperature core.
Approximately 30M degrees kelvin. This means that the star
lowers the temperature by shedding subatomic particles called
neutrinos and does so at a high speed. Because of the high
temperature, gamma-rays are able to pass near electrons and then
produce a pair of neutrinos. What this then does and why it works
is because the neutrinos have a very weak reaction with matter
which then leads to them immediately escaping the white dwarf star,
which then causes energy to be eliminated. The cooling process
can however be halted by another process called crystallization.
This means that the ions arrange themselves in what is referred to
as an ionic lattice. This causes the cooling process to abate up
to 30% and occurs when the temperature falls below a certain point.
The first knowledge of the existence of the white dwarf stars began in the year of 1850. The star was named Sirius B. What set it apart from Sirius A was that Sirius B 10.000 times more imperceptible than Sirius A as well as it had a temperature that measured to be approximately 10.000K. This combination did not make sense for a star in the sense of the luminosity to mass relation. That indicated that the star had to be incredibly small and dense.