The reason behind the dense matter of White Dwarf: Degeneracy Pressure

In 1910 , the astronomers discovered a new type of star and by 1922 it was named as ‘white dwarf’, and at that time they observed it was different from other stars. It had some questionable properties. The materialistic composition of the white dwarf seemed far too dense for classical physics approach, to explain: how it was able to shine at all?
Serious B ( the closest white dwarf star) has a mass of the Sun confined within a volume which is lesser than the Earth. Considering the fact that the Sun is about 3,30,000 times as massive as earth, that means it is an extremely physical condition indeed! For easy understanding, White dwarf ‘material’ is so dense that a teaspoon would weighs 16 tons
on earth. At that time, it was far denser than anything physicists had ever seen. The perplexing thing about the white dwarf was that though stars were supposed to to be burning gases of ions (known as plasma), but if it was some kind of extremely dense solid:how could it was shining? But later found that it was indeed a plasma not a solid , but extremely dense. The question was solid , but extremely dense. The question was
how something could be this dense and not collapses on itself due to its own gravity.
The answer is white dwarf are not simple classical gases but actually Fermi gases. In other words, a white dwarf is cluster of gases of identical fermions. Specifically, the gas of electrons. At high temperature and low pressure, a gas of electrons behaves as classical gas because there are many more states available than there are electrons but in case of white dwarf since the pressure is so high that it gets packed into a very small volume and behaves as a gas of fermions. Fermions follow the Fermi- Dirac statistics which states that, No particle can occupy the same state. Therefore, all electrons
can not occupy the lowest-energy or ground state, some of them had to occupy higher-energy states, forming a band of lowest available energy states. Thus, even at the absolute zero temperature the system still have significant amount of energy. This results an emergent pressure called Electron Degeneracy Pressure,which avoids the white dwarf from collapsing due to its gravity.

Titiksha Kumari
IISER Bhopal
“How do we know that all electrons are identical?Part 2”

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