Answer to Question #87202 in Astronomy | Astrophysics for Amit

Question

Explain the concept of degeneracy pressure. What role does it play in the evolution of a star after its death?

Answer 1

A pressure exerted by dense material consisting of fermions is called a degeneracy pressure. This pressure is explained in terms of the Pauli Exclusion Principle, which requires that no two fermions be in the same quantum state. The phenomenon can be explained on the example of electron degeneracy pressure. The Pauli Exclusion Principle forbids electrons (and all fermions with half integer spin including neutron) occupying the same state. The number of available low energy states is too small and many electrons are forced into high energy states. When this happens the electrons are said to be degenerate. These high energy electrons make a significant contribution to the pressure. This additional pressure doesn't go down as the star cools. This pressure is known as electron degeneracy pressure and it is the force that supports white dwarf stars against their own gravity.

If the star is more massive, the Fermi energy goes up and it becomes possible to absorb the electrons into the nucleons, converting protons into neutrons. The electrons disappear this way, and the star collapses suddenly down to a size for which the degeneracy pressure of the neutrons stops the collapse. Some white dwarfs stay at earth size for a long time as they suck in mass from their surroundings. When they have acquired enough mass, they collapse to form a neutron star and explode as supernova