Nuclear matter is an idealized system of interacting nucleons ( protons and

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

s) that exists in several phases of

exotic matter There are several proposed types of exotic matter: * Hypothetical particles and states of matter that have "exotic" physical properties that would violate known laws of physics, such as a particle having a negative mass. * Hypothetical partic ...

that, as of yet, are not fully established. It is ''not'' matter in an

atomic nucleus The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron ...

, but a hypothetical substance consisting of a huge number of protons and neutrons held together by only

nuclear force The nuclear force (or nucleon–nucleon interaction, residual strong force, or, historically, strong nuclear force) is a force that acts between the protons and neutrons of atoms. Neutrons and protons, both nucleons, are affected by the nucle ...

s and ''no'' Coulomb forces. Volume and the number of particles are infinite, but the ratio is finite. Infinite volume implies no surface effects and translational invariance (only differences in position matter, not absolute positions). A common idealization is ''symmetric nuclear matter'', which consists of equal numbers of protons and neutrons, with no

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s. When nuclear matter is compressed to sufficiently high density, it is expected, on the basis of the

asymptotic freedom In quantum field theory, asymptotic freedom is a property of some gauge theories that causes interactions between particles to become asymptotically weaker as the energy scale increases and the corresponding length scale decreases. Asymptotic fre ...

of quantum chromodynamics, that it will become

quark matter Quark matter or QCD matter (quantum chromodynamic) refers to any of a number of hypothetical phases of matter whose degrees of freedom include quarks and gluons, of which the prominent example is quark-gluon plasma. Several series of conferences ...

, which is a degenerate

Fermi gas An ideal Fermi gas is a state of matter which is an ensemble of many non-interacting fermions. Fermions are particles that obey Fermi–Dirac statistics, like electrons, protons, and neutrons, and, in general, particles with half-integer sp ...

of quarks. Neutron star structure

Some authors use "nuclear matter" in a broader sense, and refer to the model described above as "infinite nuclear matter", and consider it as a "toy model", a testing ground for analytical techniques. However, the composition of a

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. w ...

, which requires more than neutrons and protons, is not necessarily locally charge neutral, and does not exhibit translation invariance, often is differently referred to, for example, as ''neutron star matter'' or ''stellar matter'' and is considered distinct from nuclear matter. In a neutron star, pressure rises from zero (at the surface) to an unknown large value in the center. Methods capable of treating finite regions have been applied to stars and to atomic nuclei. One such model for finite nuclei is the

liquid drop model In nuclear physics, the semi-empirical mass formula (SEMF) (sometimes also called the Weizsäcker formula, Bethe–Weizsäcker formula, or Bethe–Weizsäcker mass formula to distinguish it from the Bethe–Weizsäcker process) is used to approxi ...

, which includes surface effects and Coulomb interactions.

References

{{Reflist Nuclear physics Phases of matter

See also

References