Degenerate matter is matter which has sufficiently high density that the dominant contribution to its pressure rises from the Pauli Exclusion Principle. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925 The pressure maintained by a body of degenerate matter is called the degeneracy pressure, and arises because the Pauli principle forbids the constituent particles to occupy identical quantum states. Any attempt to force them close enough together that they are not clearly separated by position must place them in different energy levels. Therefore, reducing the volume requires forcing many of the particles into higher-energy quantum states. This requires additional compression force, and is manifest as a resisting pressure. The species of fermion are sometimes identified, so that we may speak of electron degeneracy pressure, neutron degeneracy pressure, and so forth. In Particle physics, fermions are particles which obey Fermi-Dirac statistics; they are named after Enrico Fermi. Electron degeneracy pressure is a consequence of the Pauli exclusion principle, which states that two Fermions cannot occupy the same Quantum state at the This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron.

Contents 1 Concept 2 Degenerate gases 2.1 Electron degeneracy 2.2 Proton degeneracy 2.3 Neutron degeneracy 2.4 Quark degeneracy 3 Speculative types of degenerate matter 3.1 Preon degeneracy 4 See also 5 External links

Concept

Imagine that there is a plasma, and it is cooled and compressed repeatedly. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound Eventually, we will not be able to compress the plasma any further, because the Exclusion Principle states that two particles cannot be in the exact same place at the exact same time. When in this state, since there is no extra space for any particles, we can also say that a particle's location is extremely defined. Therefore, since (according to the Heisenberg Uncertainty Principle) uncertainty in momentum × uncertainty in space = Planck's Constant/4π, then we must say that their momentum is extremely uncertain since the molecules are located in a very confined space. In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain Therefore, even though the plasma is cold, the molecules must be moving very fast on average. This leads to the conclusion that if you want to compress an object into a very small space, you must use tremendous force to control its particles' momentum.

Unlike a classical ideal gas, whose pressure is proportional to its temperature (PV = NkT, where P is pressure, V is the volume, N is the number of particles (typically atoms or molecules), k is Boltzmann's constant, and T is temperature), the pressure exerted by degenerate matter depends only weakly on its temperature. This page is about the physical properties of gas as a state of matter Bridge from macroscopic to microscopic physics Boltzmann's constant k is a bridge between Macroscopic and microscopic physics In particular, the pressure remains nonzero even at absolute zero temperature. At relatively low densities, the pressure of a fully degenerate gas is given by P = Kn^{5 / 3}, where K depends on the properties of the particles making up the gas. At very high densities, where most of the particles are forced into quantum states with relativistic energies, the pressure is given by P = K'n^{4 / 3}, where K' again depends on the properties of the particles making up the gas.

Degenerate matter still has normal thermal pressure, but at high densities the degeneracy pressure dominates. Thus, increasing the temperature of degenerate matter has a minor effect on total pressure until the temperature rises so high that thermal pressure again dominates total pressure.

Exotic examples of degenerate matter include neutronium, strange matter, metallic hydrogen and white dwarf matter. Neutronium is a term originally used in Science fiction and in popular literature to refer to an extremely Dense phase of matter composed primarily of For the physics concept see Strange matter. Strange Matter is a Children's book series created by Marty M Metallic hydrogen results when Hydrogen is sufficiently Compressed and undergoes a phase change it is an example of Degenerate matter. A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. Degeneracy pressure contributes to the pressure of conventional solids, but these are not usually considered to be degenerate matter as a significant contribution to their pressure is provided by the interplay between the electrical repulsion of atomic nuclei and the screening of nuclei from each other by electrons allocated among the quantum states determined by the nuclear electrical potentials. A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom Potential energy can be thought of as Energy stored within a physical system In metals it is useful to treat the conduction electrons alone as a degenerate, free electron gas while the majority of the electrons are regarded as occupying bound quantum states. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across In Science and engineering, a conductor is a material which contains movable Electric charges. This contrasts with the case of the degenerate matter that forms the body of a white dwarf where all the electrons would be treated as occupying free particle momentum states.

Degenerate gases

Degenerate gases are gases composed of fermions that have a particular configuration which usually forms at high densities. In Particle physics, fermions are particles which obey Fermi-Dirac statistics; they are named after Enrico Fermi. Fermions are subatomic particles with half-integer spin. In Particle physics, fermions are particles which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In Atomic physics, the spin quantum number is a Quantum number that parameterizes the intrinsic Angular momentum (or spin angular momentum or simply Their behaviour is regulated by a set of quantum mechanical rules called the Fermi-Dirac statistics. In Statistical mechanics, Fermi-Dirac statistics is a particular case of Particle statistics developed by Enrico Fermi and Paul Dirac that One particular rule is the Pauli exclusion principle that states that there can be only one fermion occupying each quantum state which also applies to electrons that are not bound to a nucleus but merely confined to a fixed volume, such as the deep interior of a star. The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925 In Quantum physics, a quantum state is a mathematical object that fully describes a quantum system. Such particles as electrons, protons, neutrons, and neutrinos are all fermions and obey Fermi-Dirac statistics.

A fermion gas in which all the energy states below a critical value, designated Fermi energy, are filled is called a fully degenerate fermion gas. The electron gas in ordinary metals and in the interior of white dwarf stars constitute two examples of a degenerate electron gas. Most stars are supported against their own gravitation by normal gas pressure. White dwarf stars are supported by the degeneracy pressure of the electron gas in their interior. A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. For white dwarfs the degenerate particles are the electrons while for neutron stars the degenerate particles are neutrons. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type

At the end of a star's life, gravity has an enormous grip on the star's core, and compresses it to where it can go no further because of degeneracy pressure. However, as the molecules' average speed approaches (within quantum uncertainty) the speed of light to make up for gravity, then degeneracy pressure can do no more, because nothing can move faster than the speed of light. If degeneracy pressure fails in this way, then the atoms crush into atomic nuclei in a degenerate electron gas, and if degeneracy pressure fails again, then the electrons will crush into the nuclei and combine with protons to become neutrons. The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom

Electron degeneracy

In ordinary gas, most of the energy levels called n-spheres, of only certain discrete energy states available to electrons, are unfilled and the electrons are free to move about. In Atomic physics, the principal quantum number symbolized as n is the first of a set of Quantum numbers (which includes the principal quantum As particle density is increased in a fixed volume, electrons progressively fill the lower energy states and additional electrons are forced to occupy states of higher energy. Therefore, degenerate gases strongly resist further compression because the electrons cannot move to lower energy levels which are already filled due to the Pauli Exclusion Principle. The degenerate electrons are locked into place because all of the lower energy shells are filled up so they no longer move freely as in a normal gas. Even though thermal energy may be extracted from the gas, it still may not cool down, since electrons cannot give up energy by moving to a lower energy state. This increases the pressure of the fermion gas termed degeneracy pressure. In a degenerate gas, the average pressure is high enough to keep material from being compressed by gravity.

Under high densities the matter becomes a degenerate gas when the electrons are all stripped from their parent atoms. In the core of a star once hydrogen burning in nuclear fusion reactions stops, it becomes a collection of positively charged ions, largely helium and carbon nuclei, floating in a sea of electrons which have been stripped from the nuclei. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Degenerate gas is an almost perfect conductor of heat and does not obey the ordinary gas laws. White dwarfs are luminous not because they are generating any energy but rather because they have trapped a large amount of heat. Normal gas exerts higher pressure when it is heated and expands, but the pressure in a degenerate gas does not depend on the temperature. When gas becomes super-compressed, particles position right up against each other to produce degenerate gas that behaves more like a solid. In degenerate gases the kinetic energies of electrons are quite high and the rate of collision between electrons and other particles is quite low, therefore degenerate electrons can travel great distances at velocities that approach the speed of light. The kinetic energy of an object is the extra Energy which it possesses due to its motion Instead of temperature, the pressure in a degenerate gas depends only on the speed of the degenerate particles; however, adding heat does not increase the speed. Pressure is only increased by the mass of the particles which increases the gravitational force pulling the particles closer together. Therefore, the phenomenon is opposite that normally found in matter where if the mass of the matter is increased, the object becomes bigger. In degenerate gas, when the mass is increased, the pressure is increased, and the particles become spaced closer together, so the object becomes smaller. Degenerate gas can be compressed to very high densities, typical values being in the range of 10⁷ grams per cubic centimeter.

There is an upper limit to the mass of an electron-degenerate object, the Chandrasekhar limit, beyond which electron degeneracy pressure cannot support the object against collapse. The Chandrasekhar limit limits the mass of bodies made from Electron-degenerate matter, a dense form of matter which consists of nuclei immersed in a gas of Electrons The limit is approximately 1. 44 solar masses for objects with compositions similar to the sun. The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. The Sun (Sol is the Star at the center of the Solar System. The mass cutoff changes with the chemical composition of the object, as this affects the ratio of mass to number of electrons present. Celestial objects below this limit are white dwarf stars, formed by the collapse of the cores of stars which run out of fuel. A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth During collapse, an electron-degenerate gas forms in the core, providing sufficient degeneracy pressure as it is compressed to resist further collapse. Above this mass limit, a neutron star (supported by neutron degeneracy pressure) or a black hole may be formed instead. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e

Proton degeneracy

Sufficiently dense matter containing protons experiences proton degeneracy pressure, in a manner similar to the electron degeneracy pressure in electron-degenerate matter: protons confined to a sufficiently small volume have a maximum uncertainty in their momentum due to the Heisenberg uncertainty principle. Because protons are much more massive than electrons, the same momentum represents a much smaller velocity for protons than for electrons. As a result, in matter with approximately equal numbers of protons and electrons, proton degeneracy pressure is much smaller than electron degeneracy pressure, and proton degeneracy is usually modeled as a correction to the equations of state of electron-degenerate matter. In Physics and Thermodynamics, an equation of state is a relation between state variables More specifically an equation of state is a thermodynamic

Neutron degeneracy

Neutron degeneracy is analogous to electron degeneracy and is demonstrated in neutron stars, which are supported by the pressure from a degenerate neutron gas. This happens when a stellar core above 1. 44 solar masses (the Chandrasekhar limit) collapses and is not halted by the degenerate electrons. The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. As the star collapses, the Fermi energy of the electrons increases to the point where it is energetically favorable for them to combine with protons to produce neutrons (via inverse beta decay, also termed "neutralization" and electron capture). The Fermi energy is a concept in Quantum mechanics usually referring to the energy of the highest occupied Quantum state in a system of Fermions at In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted Electron capture (sometimes called inverse beta decay) is a Decay mode for Isotopes that will occur when there are too many Protons in the The result of this collapse is an extremely compact star composed of nuclear matter, which is dominantly a degenerate neutron gas, sometimes called neutronium, with a small admixture of degenerate proton and electron gases. Nuclear matter is a phase of matter that consists of Protons and Neutrons compressed to the point where they form a degenerate Fermi gas.

Neutrons in a degenerate neutron gas are spaced much more closely than electrons in an electron-degenerate gas, because the more massive neutron has a much shorter wavelength at a given energy. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. In the case of neutron stars and white dwarf stars, this is compounded by the fact that the pressures within neutron stars are much higher than those in white dwarfs. The pressure increase is caused by the fact that the compactness of neutron stars causes gravitational forces to be much higher than in a less compact body with similar mass, resulting in a star on the order of a thousand times smaller than a white dwarf.

There is an upper limit to the mass of a neutron-degenerate object, the Tolman-Oppenheimer-Volkoff limit, which is analogous to the Chandrasekhar limit for electron-degenerate objects. The Tolman-Oppenheimer-Volkoff ( TOV) limit is an upper bound to the mass of stars composed of neutron-degenerate matter ( Neutron stars. The precise limit is unknown, as it depends on the equations of state of nuclear matter, for which a highly accurate model is not yet available. In Physics and Thermodynamics, an equation of state is a relation between state variables More specifically an equation of state is a thermodynamic Above this limit, a neutron star may collapse into a black hole, or into other, denser forms of degenerate matter (such as quark matter) if these forms exist and have suitable properties (mainly related to degree of compressibility, or "stiffness", described by the equations of state).

Quark degeneracy

At densities greater than those supported by neutron degeneracy, quark matter is expected to occur. Quark matter or QCD matter (see QCD) refers to any of a number of theorized phases of matter whose degrees of freedom include Quarks and Gluons Several variations of this have been proposed that represent quark-degenerate states. Strange matter is a degenerate gas of quarks that is often assumed to contain strange quarks in addition to the usual up and down quarks. For the physics concept see Strange matter. Strange Matter is a Children's book series created by Marty M The strange quark is a second- generation Quark with a charge of &minus(1/3 e and a strangeness of &minus1 The up quark is a particle described by the Standard Model theory of Physics. The down quark is a first-generation Quark with a charge of -(1/3 e. Color superconductor materials are degenerate gases of quarks in which quarks pair up in a manner similar to Cooper pairing in electrical superconductors. Color superconductivity is a phenomenon predicted to occur in quark matter if the Baryon density is sufficiently high (well above nuclear density and the temperature In Condensed matter physics, a Cooper pair is the name given to electrons that are bound together at low temperatures in a certain manner first described in 1956 by Superconductivity is a phenomenon occurring in certain Materials generally at very low Temperatures characterized by exactly zero electrical resistance The equations of state for the various proposed forms of quark-degenerate matter vary widely, and are usually also poorly defined, due to the difficulty modeling strong force interactions. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and

Quark-degenerate matter may occur in the cores of neutron stars, depending on the equations of state of neutron-degenerate matter. It may also occur in hypothetical quark stars, formed by the collapse of objects above the Tolman-Oppenheimer-Volkoff mass limit for neutron-degenerate objects. A quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter. The Tolman-Oppenheimer-Volkoff ( TOV) limit is an upper bound to the mass of stars composed of neutron-degenerate matter ( Neutron stars. Whether quark-degenerate matter forms at all in these situations depends on the equations of state of both neutron-degenerate matter and quark-degenerate matter, both of which are poorly known.

Speculative types of degenerate matter

Preon degeneracy

Preons are subatomic particles proposed to be the constituents of quarks, which become composite particles in preon-based models. In Particle physics, preons are postulated "point-like" particles conceived to be subcomponents of Quarks and Leptons The word was coined In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. If preons exist, preon-degenerate matter might occur at densities greater than that which can be supported by quark-degenerate matter. The properties of preon-degenerate matter depend very strongly on the model chosen to describe preons, and the existence of preons is not assumed by the majority of the scientific community, due to conflicts between the preon models originally proposed and experimental data from particle accelerators.

See also

• Compact star
• White dwarf
• Neutron star - neutronium
• Quark star - QCD matter
• Preon star - preon
• Pauli exclusion principle
• Uncertainty principle

External links

• Detailed mathematical explanation of degenerate gases
• Mass-radius diagram of degenerate star types

In Astronomy, the term compact star (sometimes compact object) is used to refer collectively to White dwarfs Neutron stars other exotic A white dwarf, also called a degenerate dwarf, is a small Star composed mostly of Electron-degenerate matter. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type A quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter. Quark matter or QCD matter (see QCD) refers to any of a number of theorized phases of matter whose degrees of freedom include Quarks and Gluons A preon star is a hypothetical Compact star made of Preons a group of Theoretical Subatomic particles that may compose Quarks In Particle physics, preons are postulated "point-like" particles conceived to be subcomponents of Quarks and Leptons The word was coined The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925 In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org