The Topic of Degeneracy Is a Very Important One, Especially in the Later Part of a Star's Life
The topic of degeneracy is a very important one, especially in the later part of a star's life. It is, however, a topic that sends quivers of apprehension down the backs of most people. It has to do with quantum mechanics, and that in itself is usually enough for most people to move on, and not learn about it. That said, it is actually quite easy to understand providing that the information given is basic, and not peppered throughout with mathematics. This is the approach I shall take. In most stars, the gas of which a star is made up will behave like an ideal gas; i.e., one that has a simple relationship between its temperature, pressure and density. To be specific, the pressure exerted by a gas is directly proportional to its temperature and density. We are all familiar with this. If a gas is compressed, it heats up; likewise, if it expands, it cools. This also happens inside a star. As the temperature rises, the core regions expand and cool, and so it can be thought of as a safety valve. However, in order for certain reactions to take place inside a star, the core is compressed to very high limits, which allows very high temperatures to be achieved. These high tempera tures are necessary in order for, say, helium nuclear reactions to take place. At such high temperatures, the atoms are ionised so that they become a soup of atomic nuclei and electrons. Inside stars, especially those where the density is approach ing very high values, say, a white dwarf star or the core of a red giant, the electrons that make up the central regions of the star will resist any further compression, and themselves set up a powerful pressure.' This is termed degeneracy, so that in a low mass red giant star, for instance, the electrons are degenerate, and the core is supported by an electron degenerate pressure.
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