In astrophysics and

nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies the ...

, nuclear pasta is a theoretical type of

degenerate matter Degenerate matter is a highly dense state of fermionic matter in which the Pauli exclusion principle exerts significant pressure in addition to, or in lieu of, thermal pressure. The description applies to matter composed of electrons, protons, n ...

that is postulated to exist within the crusts of

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 ...

s. If it exists, nuclear pasta would be the strongest material in the universe. Between the surface of a neutron star and the

quark–gluon plasma Quark–gluon plasma (QGP) or quark soup is an interacting localized assembly of quarks and gluons at thermal (local kinetic) and (close to) chemical (abundance) equilibrium. The word ''plasma'' signals that free color charges are allowed. In a ...

at the core, at matter densities of 10¹⁴ g/cm³, nuclear attraction and

Coulomb repulsion Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is conventiona ...

forces are of comparable magnitude. The competition between the forces leads to the formation of a variety of complex structures assembled from

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 and protons. Astrophysicists call these types of structures ''nuclear pasta'' because the geometry of the structures resembles various types of

pasta Pasta (, ; ) is a type of food typically made from an unleavened dough of wheat flour mixed with water or eggs, and formed into sheets or other shapes, then cooked by boiling or baking. Rice flour, or legumes such as beans or lentils, ar ...

Formation

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 ...

s form as remnants of massive stars after a supernova event. Unlike their progenitor star, neutron stars do not consist of a gaseous plasma. Rather, the intense gravitational attraction of the compact mass overcomes the

electron degeneracy pressure Electron degeneracy pressure is a particular manifestation of the more general phenomenon of quantum degeneracy pressure. The Pauli exclusion principle disallows two identical half-integer spin particles (electrons and all other fermions) from si ...

and causes

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...

to occur within the star. The result is a compact ball of nearly pure neutron matter with sparse

protons A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mas ...

and

electrons 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 ...

interspersed, filling a space several thousand times smaller than the progenitor star. At the surface, the pressure is low enough that conventional nuclei, such as

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

and

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

, can exist independently of one another and are not crushed together due to the mutual

of their nuclei. At the core, the pressure is so great that this Coulomb repulsion cannot support individual nuclei, and some form of ultra-dense matter, such as the theorized

, should exist. The presence of a small population of protons is essential to the formation of nuclear pasta. The nuclear attraction between protons and neutrons is greater than the nuclear attraction of two protons or two neutrons. Similar to how neutrons act to stabilize heavy nuclei of conventional atoms against the electric repulsion of the protons, the protons act to stabilize the pasta phases. The competition between the electric repulsion of the protons, the attractive force between nuclei, and the pressure at different depths in the star lead to the formation of nuclear pasta.

Phases

While nuclear pasta has not been observed in a neutron star, its phases are theorized to exist in the inner crust of neutron stars, forming a transition region between the conventional matter at the surface and the ultra-dense matter at the core. All phases are expected to be amorphous, with a heterogeneous

charge distribution In electromagnetism, charge density is the amount of electric charge per unit length, surface area, or volume. Volume charge density (symbolized by the Greek letter ρ) is the quantity of charge per unit volume, measured in the SI system in co ...

. Towards the top of this transition region, the pressure is great enough that conventional nuclei will be condensed into much more massive semi-spherical collections. These formations would be unstable outside the star, due to their high neutron content and size, which can vary between tens and hundreds of

nucleons In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number (nucleon number). Until the 1960s, nucleons we ...

. This semispherical phase is known as the ''

gnocchi Gnocchi ( , , ; singular ''gnocco'') are a varied family of dumpling in Italian cuisine. They are made of small lumps of dough most traditionally composed of a simple combination of wheat flour, egg, salt, and potato. Variations of the dish sup ...

phase''. When the gnocchi phase is compressed, as would be expected in deeper layers of the crust, the electric repulsion of the protons in the gnocchi is not fully sufficient to support the existence of the individual spheres, and they are crushed into long rods, which, depending on their length, can contain many thousands of nucleons. These rods are known as the ''

spaghetti Spaghetti () is a long, thin, solid, cylindrical pasta.spaghetti
Dictionary.com. Dictionary.com Unabridg ...

phase''. Further compression causes the spaghetti phase rods to fuse and form sheets of nuclear matter called the ''

lasagna Lasagna (, also , also known as lasagne, ) is a type of pasta, possibly one of the oldest types, made of very wide, flat sheets. Either term can also refer to an Italian dish made of stacked layers of lasagna alternating with fillings such as ...

phase''. Further compression of the lasagna phase yields the uniform nuclear matter of the outer core. Progressing deeper into the inner crust, those holes in the nuclear pasta change from being cylindrical, called by some the ''

bucatini Bucatini (), also known as perciatelli (), are a thick spaghetti-like pasta with a hole running through the center. They are common throughout Lazio, particularly Rome. The similar ziti are long hollow rods which are also smooth in texture an ...

phase'' or ''antispaghetti phase'', into scattered spherical holes, which can be called the ''

Swiss cheese Swiss cheese may refer to: Cheese * List of Swiss cheeses (from Switzerland) * Swiss-type cheeses or Alpine cheeses, a class of cooked pressed cheeses now made in many countries * Swiss cheese (North America), any of several related varieties o ...

phase''. The nuclei disappear at the crust–core interface, transitioning into the liquid neutron core of the star. The pasta phases also have interesting topological properties characterized by

homology groups In mathematics, homology is a general way of associating a sequence of algebraic objects, such as abelian groups or modules, with other mathematical objects such as topological spaces. Homology groups were originally defined in algebraic topolog ...

. For a typical neutron star of 1.4 solar masses () and 12 km radius, the nuclear pasta layer in the crust can be about 100 m thick and have a mass of about 0.01 . In terms of mass, this is a significant portion of the crust of a neutron star.

References

{{Portal bar, Physics, Astronomy, Stars, Spaceflight, Outer space, Solar System, Science Exotic matter Neutron stars Phases of matter Amorphous solids Metaphors referring to food and drink

Formation

Phases

See also

References