Degenerate matter
Degenerate matter (also degenerate matter ) is matter in a state that deviates from the behavior known in classical physics due to quantum mechanical effects . This generally occurs at very high densities or at very low temperatures , but it also applies under normal conditions to the conduction electrons in metals . The term degeneracy has a different meaning here than for degenerate energy levels .
Degenerate matter is widespread in the universe . It is estimated that about 10% of all stars are white dwarfs , which are made up of degenerate matter (mainly oxygen and carbon ). In white dwarfs the electrons are degenerate, in neutron stars the neutrons .
Degenerate fermion gas
If fermions (e.g. protons , electrons or neutrons) are concentrated too much in stars, gravity , which acts inwards and leads to higher density, is countered by a degeneracy pressure (also known as Fermi pressure ). The degeneracy pressure counteracts the gravitational pressure and is caused by the Pauli principle , which prohibits two fermions from being able to assume an identical quantum state . Therefore, a further compression would mean that fermions would have to move into higher energy states , so that further fermions could enter the volume under consideration and thus increase the density.
The (quasi) free (conduction) electron gas in common metals is also degenerate in this sense; H. many metallic properties (such as electrical or thermal conductivity) can not be described without quantum mechanics .
Degenerate matter in stars
White dwarfs are stabilized by the degenerative pressure of their electron gas.
In a physical binary star system , a white dwarf can grow further through an accretion flow from its companion star. When its mass reaches the Chandrasekhar limit , the degeneracy pressure can no longer compensate for the gravitational pressure. One could therefore assume that a neutron star would then be formed . Instead, however, the rising temperature and density lead to new nuclear fusion reactions and a type Ia supernova is created , because the white dwarf, unlike a neutron star, still consists of fusible matter.
Individual evidence
- ↑ J. Krautter et al. a .: Meyers Handbuch Weltall. Meyers Lexikonverlag 1994, ISBN 3-411-07757-3 , p. 291 ff.