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Strange matter
Strange matter is a particular form of quark matter, usually thought of as a “liquid” of up, down and strange quarks. 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. At high enough density, strange matter is expected to be color superconducting. 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).
==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〔J. Madsen, “Physics and astrophysics of strange quark matter” (arXiv:astro-ph/9809032 ), Lect. Notes Phys. 516:162-203 (1999)〕〔F. Weber, “Strange quark matter and compact stars”, (arXiv:astro-ph/0407155 ), Prog.Part.Nucl.Phys.54:193-288,2005.〕
# The broader meaning is simply 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 narrower meaning is that quark matter is ''more stable than nuclear matter'', i.e. that the true ground state of matter is quark matter. The idea that this could happen is the “strange matter hypothesis” of Bodmer〔A. Bodmer “Collapsed Nuclei” (Phys. Rev. D4, 1601 (1971) )〕 and Witten.〔Edward Witten, “Cosmic Separation Of Phases” (Phys. Rev. D30, 272 (1984) )〕 In this definition, the critical pressure is zero. 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.e. strangelets.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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