The continent of stability is a hypothesised large group of

nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of protons, ''Z'', their number of neutrons, ''N'', and their nuclear energy state. The word ''nuclide'' was coined by Truman ...

s with masses greater than 300 daltons that is stable against radioactive decay, consisting of freely flowing up quarks and down quarks rather than up and down quarks bound into protons and neutrons. Matter containing these nuclides is termed up-down quark matter (udQM). The continent of stability is named in analogy with the island of stability. However, if it exists, the range of charge and mass will be much greater than in the island. Quark matter composed of up quarks and down quarks is predicted to be a lower energy state than that which contains

strange quark The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons ( ...

s (

strange quark matter Strange matter (or strange quark matter) is quark matter containing strange quarks. In nature, strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtomete ...

), and also lower than the combination of quarks in the form of

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the ele ...

s found in normal atomic nuclei if there are over 300 protons and neutrons. The lower limit of 300 was calculated based on a surface tension model, where the surface has a higher energy than the interior of the piece of quark matter. In order to be the absolutely more stable form, the energy must be lower than that of the most stable normal matter, that is 930 MeV per

baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classified ...

. If these quark matter nuclides exist, they would be stable against

fission Fission, a splitting of something into two or more parts, may refer to: * Fission (biology), the division of a single entity into two or more parts and the regeneration of those parts into separate entities resembling the original * Nuclear fissio ...

, as fission would increase the surface. The quark matter nuclide could absorb neutrons resulting in an increase in its mass. ChargeVersusBaryonNumber

The boundary to the continent of stability is determined by the situations where the Coulomb energy due to electric charge overcomes the

binding energy In physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly use ...

, or where decay into atomic nuclei results in lower energy. The lowest energy mass number is proportional to the cube of the charge (atomic number). However, a range of charges is stable for each mass, and the range increases as the mass increases. This can result in very heavy nuclides with atomic numbers the same as existing known elements, and even zero charge pieces of quark matter. A proposed alternative form of quark matter known as

strangelet A strangelet (pronounced ) is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter, small enough to be c ...

s contains

s in addition to the up and down quarks. This would be neutral in charge, and thus not form atoms. udQM is probably lower energy than strangelets (uds-matter). At the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundred ...

, the

ATLAS Collaboration ATLAS is the largest general-purpose particle detector experiment at the Large Hadron Collider (LHC), a particle accelerator at CERN (the European Organization for Nuclear Research) in Switzerland. The experiment is designed to take advantage of ...

is attempting to observe this kind of matter.

Other properties

Electron-positron pairs will form in the high charge field via the

Schwinger mechanism The Schwinger effect is a predicted physical phenomenon whereby matter is created by a strong electric field. It is also referred to as the Sauter–Schwinger effect, Schwinger mechanism, or Schwinger pair production. It is a prediction of quantum ...

when the electric charge of udQM is larger than 163, at which the baryon number is 609. The smallest stable udQM against neutron emission would be at baryon number 39.

Formation in nature

udQM could be possibly formed during a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

core collapse from conversion of superheavy nuclei. In this environment there is a high density of electrons and electron neutrinos present. The udQM would then end up in

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. white ...

s. udQM nuclides may be detectable in cosmic rays. A star containing a large proportion of udQM is called a ud quark star (or udQS). Heavy neutron stars may convert into this star type. Whether they do may be verified by detecting binary compact star collisions.

References

{{reflist Periodic table Isotopes Nuclear physics Quantum chromodynamics Quark matter