Under extremely high pressure, as in the cores of dead stars, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as degenerate matter, these are supported mainly by quantum mechanical effects. “degenerate” refers to two states that have identical energy and are thus interchangeable. It is supported by the Pauli exclusion principle, which prevents two fermionic particles from occupying the same quantum state. Unlike regular plasma, degenerate plasma expands little when heated, because there are simply no momentum states left. Consequently, degenerate stars collapse into very high densities. More massive degenerate stars are smaller, because the gravitational force increases, but pressure does not increase proportionally.
Electron-degenerate matter is found inside white dwarf stars. Electrons remain bound to atoms and are able to transfer to adjacent atoms. Neutron-degenerate matter is found in neutron stars. High gravitational pressure compresses atoms so strongly that the electrons are forced to combine with protons via inverse beta-decay, resulting in a superdense conglomeration of neutrons. Usually free neutrons outside an atomic nucleus will decay with a half life of approximately 10 minutes, but in a neutron star, the decay is overtaken by inverse decay. Cold degenerate matter is also present in planets such as Jupiter and in even more massive brown dwarfs, they are expected to have a core with metallic hydrogen. Because of the degeneracy, more massive brown dwarfs are not significantly larger. In metals, the electrons can be modeled as a degenerate gas which is moving in a lattice of non-degenerate positive ions.
Quark matter
Particle collision cern poster
In regular cold matter, quarks, fundamental particles of nuclear matter, are confined by the strong force into hadrons that consist of 2– 4 quarks, such as protons and neutrons. quantum chromodynamical (QCD) matter or Quark matter is a group of phases where the strong force is overcome and they are deconfined and free to move. Quark matter phases occur at extremely high densities or temperatures, and there are no known ways to produce them in equilibrium in laboratory; in ordinary conditions, any quark matter formed immediately undergoes radioactive decay
Strange matter is a type of quark matter that is suspected to exist inside some neutron stars close to the Tolman–Oppenheimer–Volkoff limit (approximately 2–3 solar masses), although there is no direct evidence of its existence. In strange matter, part of the energy available manifests as strange quarks, a heavier analogue of the common down quark. It may be stable at lower energy states once formed, although this is not known.
Quark–gluon plasma is a very high-temperature phase in which quarks become free and able to move freely, rather than being perpetually bound into particles, in a sea of gluons, subatomic particles that transmit the strong force that binds quarks together. This is analogous to the liberation of electrons from atoms in a plasma. This state is briefly attainable in extremely high-energy heavy ion collisions in particle accelerators, and allows scientists to observe the properties of individual quarks, and not just theorize. Quark–gluon plasma was discovered at CERN in 2000. Unlike plasma, which flows like a gas, interactions within QGP are strong and it flows like a liquid.
At high densities but relatively low temperatures, quarks are theorized to form a quark liquid whose nature is presently unknown. It forms a distinct color-flavor locked (CFL) phase at even higher densities. This phase is superconductive for color charge. These phases may occur in neutron stars but they are presently theoretical.
Color-glass condensate
It is a type of matter theorized to exist in atomic nuclei traveling near the speed of light. According to Einstein’s theory of relativity, a high-energy nucleus appears length contracted, or compressed, along its direction of motion, due to which the gluons inside the nucleus appear to a stationary observer as a “gluonic wall” traveling near the speed of light. At very high energies, the density of the gluons in this wall is seen to increase highly. Unlike the quark–gluon plasma produced in the collision of such walls, the color-glass condensate describes the walls themselves, and is an intrinsic property of the particles that can only be observed under high-energy conditions such as those at RHIC and possibly at the Large Hadron Collider as well.
Very high energy states
Various theories predict new states of matter at very high energies. An unknown state has created the baryon asymmetry in the universe, but little is known about it. In string theory, a Hagedorn temperature is predicted for superstrings at about 1030 K, where superstrings are copiously produced. At Planck temperature (1032 K), gravity becomes a significant force between individual particles. No current theory can describe these states and they cannot be produced with any foreseeable experiment. However, these states are important in cosmology because the universe may have passed through these states in the Big Bang.
The gravitational singularity predicted by general relativity to exist at the center of a black hole is not a phase of matter; it is not a material object at all (although the mass-energy of matter contributed to its creation) but rather a property of spacetime. Because spacetime breaks down there, the singularity should not be thought of as a localized structure, but as a global, topological feature of spacetime.It has been argued that elementary particles are fundamentally not material, either, but are localized properties of spacetime. In quantum gravity, singularities may in fact mark transitions to a new phase of matter.
Other proposed states
Supersolid
It is a spatially ordered material (that is, a solid or crystal) with superfluid properties. Similar to a superfluid, a supersolid is able to move without friction also it retains a rigid shape. Although a supersolid is a solid, it exhibits so many characteristic properties different from other solids that many argue that, it is another state of matter.
String-net liquid
Simulated Large Hadron Collider CMS particle detector data depicting a Higgs boson produced by colliding protons decaying into hadron jets and electrons
In a string-net liquid, atoms have apparently unstable arrangement, like a liquid, but are still consistent in overall pattern, like a solid. When in a normal solid state, the atoms of matter align themselves in a grid pattern, so that the spin of an electron is the opposite of the spin of all electrons touching it. But in a string-net liquid, the atoms are arranged in some pattern that requires some electrons to have neighbors with the same spin. This gives rise to curious properties, as well as supporting some unusual proposals about the fundamental conditions of the universe itself.
Superglass
A superglass is a phase of matter characterized, at the same time, by superfluidity and a frozen amorphous structure.
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