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{{short description|Degenerate matter made from strange quarks}}
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{{Refimprove|date=October 2016}} {{Refimprove|date=October 2017}}


'''Strange matter''' is a particular form of ], usually thought of as a "liquid" of ], ] and ]s. It is to be contrasted with ], which is a liquid of ]s and ]s (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 ].{{citation needed|date=February 2019}} Strange matter is hypothesized to occur in the core of ]s, or, more speculatively, as isolated droplets that may vary in size from ]s (]s) to kilometers (]s). '''Strange matter''' (or '''strange quark matter''') is ] containing ]s. In extreme environments, strange matter is hypothesized to occur in the core of ]s, or, more speculatively, as isolated droplets that may vary in size from ]s (]s) to kilometers, as in the hypothetical ]. At high enough density, strange matter is expected to be ].{{citation needed|date=February 2019}}


Ordinary ], also referred to as atomic matter, is composed of atoms, with nearly all matter concentrated in the atomic nuclei. ] is a liquid composed of ]s and ]s, and they are themselves composed of ] and ]. Quark matter is a ] composed entirely of ]s. When quark matter does not contain strange quarks, it is sometimes referred to as non-strange quark matter.
== Two meanings of the term "strange matter" ==


==Context==
In ] and ], the term is used in two ways, one broader and the other more specific<ref name='Madsen:1998'>{{Cite book|arxiv=astro-ph/9809032|doi=10.1007/BFb0107314|chapter=Physics and astrophysics of strange quark matter|title=Hadrons in Dense Matter and Hadrosynthesis|volume=516|pages=162–203|series=Lecture Notes in Physics|year=1999|last1=Madsen|first1=Jes|isbn=978-3-540-65209-0}}</ref><ref name='Weber'>{{Cite journal|arxiv=astro-ph/0407155|doi=10.1016/j.ppnp.2004.07.001|title=Strange quark matter and compact stars|journal=Progress in Particle and Nuclear Physics|volume=54|issue=1|pages=193–288|year=2005|last1=Weber|first1=F.|bibcode=2005PrPNP..54..193W}}.</ref> In ] and ], the term 'strange matter' is used in two different contexts, one broader and the other more specific and hypothetical:<ref name="Madsen:1998">{{Cite book |last1=Madsen |first1=Jes |title=Hadrons in Dense Matter and Hadrosynthesis |year=1999 |isbn=978-3-540-65209-0 |series=Lecture Notes in Physics |volume=516 |pages=162–203 |chapter=Physics and astrophysics of strange quark matter |doi=10.1007/BFb0107314 |arxiv=astro-ph/9809032 |s2cid=16566509 }}</ref><ref name="Weber">{{Cite journal |last1=Weber |first1=F. |year=2005 |title=Strange quark matter and compact stars |journal=Progress in Particle and Nuclear Physics |volume=54 |issue=1 |pages=193–288 |arxiv=astro-ph/0407155 |bibcode=2005PrPNP..54..193W |doi=10.1016/j.ppnp.2004.07.001 |s2cid=15002134 }}.</ref>


# The broader meaning is simply quark matter that contains three ]: up, down, and strange. In this definition, there is a critical pressure and an associated critical density, and when nuclear matter (made of ] and ]) is compressed beyond this density, the protons and neutrons dissociate into quarks, yielding quark matter (probably strange matter). # In the broader context, our current understanding of the ] predicts that strange matter could be created when nuclear matter (made of ] and ]) is compressed beyond a critical density. At this critical pressure and density, the protons and neutrons dissociate into quarks, yielding quark matter and potentially 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 ]<ref name='Bodmer'>{{Cite journal|doi=10.1103/PhysRevD.4.1601|title=Collapsed Nuclei|journal=Physical Review D|volume=4|issue=6|pages=1601–1606|year=1971|last1=Bodmer|first1=A. R.|bibcode=1971PhRvD...4.1601B}}</ref> and ].<ref name='Witten'>{{Cite journal|first=Edward|last= Witten|title=Cosmic separation of phases|journal=Physical Review D|volume=30|issue=2|pages=272–285|doi=10.1103/PhysRevD.30.272|author-link=Edward Witten|year=1984|bibcode=1984PhRvD..30..272W}}</ref> 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 ], and given enough time (or the right external stimulus) would decay into droplets of strange matter, i.e. strangelets. # A more specific hypothesis is that quark matter is the true ground state of all matter, and thus more stable than ordinary nuclear matter. This idea is known as the "strange matter hypothesis", or the ]–] assumption.<ref name="Bodmer">{{Cite journal |last1=Bodmer |first1=A. R. |date=September 1971 |title=Collapsed Nuclei |url=https://ui.adsabs.harvard.edu/abs/1971PhRvD...4.1601B/abstract |journal=Physical Review D |volume=4 |issue=6 |pages=1601–1606 |bibcode=1971PhRvD...4.1601B |doi=10.1103/PhysRevD.4.1601 |access-date=2022-03-22 |archive-date=2022-01-20 |archive-url=https://web.archive.org/web/20220120042524/https://ui.adsabs.harvard.edu/abs/1971PhRvD...4.1601B/abstract |url-status=live }}</ref><ref name="Witten">{{Cite journal |last=Witten |first=Edward |author-link=Edward Witten |date=July 1984 |title=Cosmic separation of phases |url=https://ui.adsabs.harvard.edu/abs/1984PhRvD..30..272W |journal=Physical Review D |volume=30 |issue=2 |pages=272–285 |bibcode=1984PhRvD..30..272W |doi=10.1103/PhysRevD.30.272 |access-date=2022-03-22 |archive-date=2022-01-25 |archive-url=https://web.archive.org/web/20220125070503/https://ui.adsabs.harvard.edu/abs/1984PhRvD..30..272W |url-status=live }}</ref> Under this hypothesis, the nuclei of the atoms we see around us are only ], even when the external critical pressure is zero, and given enough time (or the right stimulus) the nuclei would decay into stable droplets of strange matter. Droplets of strange matter are also referred to as strangelets.


== Strange matter that is only stable at high pressure == == Stability of strange matter only at high pressure ==


Under the broader definition, strange matter might occur inside neutron stars, if the pressure at their core is high enough (i.e. above the critical pressure). At the sort of densities and high pressures 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. ] quarks and heavier quarks would only occur at much higher densities. In the general context, strange matter might occur inside neutron stars, if the pressure at their core is high enough to provide a sufficient gravitational force (i.e. above the critical pressure). At the sort of densities and high pressures 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. ] quarks and heavier quarks would only occur at much higher densities.


Strange matter comes about as a way to relieve ]. The ] forbids fermions such as quarks from occupying the same position and energy level. When the particle density is high enough that all energy levels below the available thermal energy are already occupied, increasing the density further requires raising some to higher, unoccupied energy levels. This need for energy to cause compression manifests as a pressure. Neutrons consist of twice as many ]s (charge −{{sfrac|1|3}}&nbsp;]) as ]s (charge +{{sfrac|2|3}}&nbsp;''e''), so the degeneracy pressure of down quarks usually dominates electrically neutral quark matter. However, when the required energy level is high enough, an alternative becomes available: half of the down quarks can be transmuted to strange quarks (charge −{{sfrac|1|3}}&nbsp;''e''). The higher rest mass of the strange quark costs some energy, but by opening up an additional set of energy levels, the average energy per particle can be lower,{{r|Madsen:1998|p=5}} making strange matter more stable than non-strange quark matter.
⚫ A neutron star with a quark matter core is often<ref name='Madsen:1998' /><ref name='Weber' /> 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{{Citation needed|date=July 2011}} that the transition to quark matter will already have occurred when the separation between the ]s becomes much smaller than their size, so the critical density must be less than about 100 times nuclear saturation density. But a more precise estimate is not yet available, because the ] that governs the behavior of quarks is mathematically intractable, and numerical calculations using ] are currently blocked by the fermion ].


⚫ A neutron star with a quark matter core is often{{r|Madsen:1998|Weber}} called a hybrid star. However, it is difficult 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 ]s becomes much smaller than their size, so the critical density must be less than about 100 times nuclear saturation density. But a more precise estimate is not yet available, because the ] that governs the behavior of quarks is mathematically intractable, and numerical calculations using ] are currently blocked by the fermion ].
⚫ 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. <!-- See ] -->


⚫ One major area of activity in neutron star physics is the attempt to find observable signatures by which we could tell whether neutron stars have quark matter (probably strange matter) in their core. <!-- See ] -->
⚫ == 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.<ref name='Witten' /> However, under this hypothesis there should be strange matter in the universe: During the merger of two neutron stars, strange matter may be ejected out into the space around the stars, which may allow for the studying of strange matter. However, the rate at which strange matter decays is unknown, and there are very few binary pairs of neutron stars nearby to the Solar System, which could make the official discovery of strange matter very difficult.

⚫ ==Stability of strange matter at zero pressure==

If the "]" 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.<ref name='Witten' /> However, under this hypothesis there should be strange matter in the universe:
# Quark stars (often called "strange stars") consist of quark matter from their core to their surface. They would be several kilometers across, and may have a very thin crust of nuclear matter.<ref name='Weber' /> # Quark stars (often called "strange stars") consist of quark matter from their core to their surface. They would be several kilometers across, and may have a very thin crust of nuclear matter.<ref name='Weber' />
# Strangelets are small pieces of strange matter, perhaps as small as nuclei. They would be produced when strange stars are formed or collide, or when a nucleus decays.<ref name='Madsen:1998' /> # ] are small pieces of strange matter, perhaps as small as nuclei. They would be produced when strange stars are formed or collide, or when a nucleus decays.<ref name='Madsen:1998' />


== See also == ==See also==
⚫ * {{annotated link|Exotic matter}}
{{div col|colwidth=25em}}
* {{annotated link|Quark star}}
⚫ * ]
* ] &ndash; subatomic signature
* ]
* {{annotated link|Strangelet}}
* ]
* {{annotated link|Quark}}
* ]
* {{annotated link|QCD matter}}
* ]
* ]
* ]
* ]
{{div col end}}


== References == ==References==
{{reflist}} {{reflist}}


{{Phase of matter}} {{Phase of matter}}
{{Stellar core collapse}}


] ]
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] ]
]

Latest revision as of 13:28, 26 December 2023

Degenerate matter made from strange quarks
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Strange matter (or strange quark matter) is quark matter containing strange quarks. In extreme environments, 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, as in the hypothetical strange stars. At high enough density, strange matter is expected to be color superconducting.

Ordinary matter, also referred to as atomic matter, is composed of atoms, with nearly all matter concentrated in the atomic nuclei. Nuclear matter is a liquid composed of neutrons and protons, and they are themselves composed of up and down quarks. Quark matter is a condensed form of matter composed entirely of quarks. When quark matter does not contain strange quarks, it is sometimes referred to as non-strange quark matter.

Context

In particle physics and astrophysics, the term 'strange matter' is used in two different contexts, one broader and the other more specific and hypothetical:

  1. In the broader context, our current understanding of the laws of nature predicts that strange matter could be created when nuclear matter (made of protons and neutrons) is compressed beyond a critical density. At this critical pressure and density, the protons and neutrons dissociate into quarks, yielding quark matter and potentially strange matter.
  2. A more specific hypothesis is that quark matter is the true ground state of all matter, and thus more stable than ordinary nuclear matter. This idea is known as the "strange matter hypothesis", or the Bodmer–Witten assumption. Under this hypothesis, the nuclei of the atoms we see around us are only metastable, even when the external critical pressure is zero, and given enough time (or the right stimulus) the nuclei would decay into stable droplets of strange matter. Droplets of strange matter are also referred to as strangelets.

Stability of strange matter only at high pressure

In the general context, strange matter might occur inside neutron stars, if the pressure at their core is high enough to provide a sufficient gravitational force (i.e. above the critical pressure). At the sort of densities and high pressures 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 quarks and heavier quarks would only occur at much higher densities.

Strange matter comes about as a way to relieve degeneracy pressure. The Pauli exclusion principle forbids fermions such as quarks from occupying the same position and energy level. When the particle density is high enough that all energy levels below the available thermal energy are already occupied, increasing the density further requires raising some to higher, unoccupied energy levels. This need for energy to cause compression manifests as a pressure. Neutrons consist of twice as many down quarks (charge −⁠1/3⁠ e) as up quarks (charge +⁠2/3⁠ e), so the degeneracy pressure of down quarks usually dominates electrically neutral quark matter. However, when the required energy level is high enough, an alternative becomes available: half of the down quarks can be transmuted to strange quarks (charge −⁠1/3⁠ e). The higher rest mass of the strange quark costs some energy, but by opening up an additional set of energy levels, the average energy per particle can be lower, making strange matter more stable than non-strange quark matter.

A neutron star with a quark matter core is often called a hybrid star. However, it is difficult 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. But a more precise estimate is not yet available, because the strong interaction that governs the behavior of quarks is mathematically intractable, and numerical calculations using lattice QCD are currently blocked by the fermion sign problem.

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

During the merger of two neutron stars, strange matter may be ejected out into the space around the stars, which may allow for the studying of strange matter. However, the rate at which strange matter decays is unknown, and there are very few binary pairs of neutron stars nearby to the Solar System, which could make the official discovery of strange matter very difficult.

Stability of strange matter 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. 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. They would be produced when strange stars are formed or collide, or when a nucleus decays.

See also

References

  1. ^ Madsen, Jes (1999). "Physics and astrophysics of strange quark matter". Hadrons in Dense Matter and Hadrosynthesis. Lecture Notes in Physics. Vol. 516. pp. 162–203. arXiv:astro-ph/9809032. doi:10.1007/BFb0107314. ISBN 978-3-540-65209-0. S2CID 16566509.
  2. ^ Weber, F. (2005). "Strange quark matter and compact stars". Progress in Particle and Nuclear Physics. 54 (1): 193–288. arXiv:astro-ph/0407155. Bibcode:2005PrPNP..54..193W. doi:10.1016/j.ppnp.2004.07.001. S2CID 15002134..
  3. Bodmer, A. R. (September 1971). "Collapsed Nuclei". Physical Review D. 4 (6): 1601–1606. Bibcode:1971PhRvD...4.1601B. doi:10.1103/PhysRevD.4.1601. Archived from the original on 2022-01-20. Retrieved 2022-03-22.
  4. ^ Witten, Edward (July 1984). "Cosmic separation of phases". Physical Review D. 30 (2): 272–285. Bibcode:1984PhRvD..30..272W. doi:10.1103/PhysRevD.30.272. Archived from the original on 2022-01-25. Retrieved 2022-03-22.
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