Strange matter is a particular form of quark matter, usually thought of as a 'liquid' of up, down, and strange quarks. 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 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. The strange quark is a second- generation Quark with a charge of &minus(1/3 e and a strangeness of &minus1 In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. It is to be contrasted with nuclear matter, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid containing only up and down quarks. Nuclear matter is a phase of matter that consists of Protons and Neutrons compressed to the point where they form a degenerate Fermi gas. This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive At high enough density, strange matter is expected to be color superconducting. 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 Strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars). 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 The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International A strangelet is a hypothetical object consisting of a bound state of roughly equal numbers of up, down, and strange Quarks The size would be A quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter.

Two meanings of the term "strange matter"

In particle physics and astrophysics, the term is used in two ways, one broader and the other more specific. Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them Astrophysics is the branch of Astronomy that deals with the Physics of the Universe, including the physical properties ( Luminosity,

1. The broader meaning is just quark matter that contains three flavors of quarks: up, down, and strange. In this definition, there is a critical pressure and an associated critical density, and when nuclear matter (made of protons and neutrons) is compressed beyond this density, the protons and neutrons dissociate into quarks, yielding quark matter (probably strange matter). The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron.
2. The narrower meaning is quark matter that is more stable than nuclear matter. The idea that this could happen is the "strange matter hypothesis" of Bodmer ^[1] and Witten ^[2]. In this definition, the critical pressure is zero: the true ground state of matter is always quark matter. The nuclei that we see in the matter around us, which are droplets of nuclear matter, are actually metastable, and given enough time (or the right external stimulus) would decay into droplets of strange matter, i. Metastability is a general scientific concept which describes states of delicate equilibrium e. strangelets. A strangelet is a hypothetical object consisting of a bound state of roughly equal numbers of up, down, and strange Quarks The size would be

Strange matter that is only stable at high pressure

Under the broader definition, strange matter might occur inside neutron stars, if the pressure at their core is high enough (i. 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 e. above the critical pressure). At the sort of densities we expect in the center of a neutron star, the quark matter would probably be strange matter. It could conceivably be non-strange quark matter, if the effective mass of the strange quark were too high. Charm and heavier quarks would only occur at much higher densities. The charm Quark is a second-generation quark with an electric charge of +(2/3 e.

A neutron star with a quark matter core is often called a hybrid star. However, it is hard to know whether hybrid stars really exist in nature because physicists currently have little idea of the likely value of the critical pressure or density. It seems plausible that the transition to quark matter will already have occurred when the separation between the nucleons becomes much smaller than their size, so the critical density must be less than about 100 times nuclear saturation density. In Physics a nucleon is a collective name for two Baryons the Neutron and the Proton. But a more precise estimate is not yet available, because the strong interaction that governs the behavior of quarks is particularly intractable, and numerical calculations using lattice QCD are currently blocked by the fermion sign problem. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and In Physics, lattice quantum chromodynamics (lattice QCD is a theory of Quarks and Gluons formulated on a space-time lattice.

One major area of activity in neutron star physics is the attempt to find observable signatures by which we could tell, from earth based observations of neutron stars, whether they have quark matter (probably strange matter) in their core.

Strange matter that is stable at zero pressure

If the "strange matter hypothesis" is true then nuclear matter is metastable against decaying into strange matter. The lifetime for spontaneous decay is very long, so we do not see this decay process happening around us. However, under this hypothesis there should be strange matter in the universe:

1. Quark stars (often called "strange stars") consist of quark matter from their core to their surface. A quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter. They would be several kilometers across, and may have a very thin crust of nuclear matter.
2. Strangelets are small pieces of strange matter, perhaps as small as nuclei. A strangelet is a hypothetical object consisting of a bound state of roughly equal numbers of up, down, and strange Quarks The size would be They would be produced when strange stars are formed or collide.

See also

• Quark matter
• Quark star
• Strangelet

Further reading

• J. 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 quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter. A strangelet is a hypothetical object consisting of a bound state of roughly equal numbers of up, down, and strange Quarks The size would be Madsen, "Physics and astrophysics of strange quark matter" Lect. Notes Phys. 516:162-203 (1999)

References

1. ^ A. Bodmer "Collapsed Nuclei" Phys. Rev. D4, 1601 (1971)
2. ^ E. Witten, "Cosmic Separation Of Phases" Phys. Rev. D30, 272 (1984)