A strangelet or "strange nugget" is a hypothetical object consisting of a bound state of roughly equal numbers of up, down, and strange quarks. 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. The size could be anything from a few femtometers across (with the mass of a light nucleus) to something much larger. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Once the size becomes macroscopic (on the order of meters across), such an object is usually called a quark star or "strange star" rather than a strangelet. A quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter. An equivalent description is that a strangelet is a small fragment of strange matter. For the physics concept see Strange matter. Strange Matter is a Children's book series created by Marty M The term "strangelet" originates with E. Farhi and R. Jaffe. Robert L Jaffe is an American physicist and the Jane and Otto Morningstar Professor of Physics at the Massachusetts Institute of Technology (MIT ^[1] Strangelets have been suggested as a dark matter candidate. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from

Contents 1 Theoretical possibility 1.1 Strange matter hypothesis 1.2 Relationship with nuclei 1.3 Size 2 Natural or artificial occurrence 2.1 Accelerator production 2.2 Space-based detection 2.3 Possible seismic detection 3 Dangers 4 Debate about the strange matter hypothesis 5 In fiction 6 References 7 External links and further reading

Theoretical possibility

Strange matter hypothesis

The main question about strangelets concerns their stability. The known particles with strange quarks are unstable because the strange quark is heavier than the up and down quarks, so strange particles, such as the Lambda particle, which contains an up, down, and strange quark, always lose their strangeness, radioactively decaying via the weak interaction to lighter particles containing only up and down quarks. In Particle physics, Lambda (Λ baryons are Baryons containing an Up quark, a Down quark, and a third quark either a Strange quark The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four Fundamental interactions of nature But states with a larger number of quarks might not suffer from this instability. This is the "strange matter hypothesis" of Bodmer ^[2] and Witten. Edward Witten (born August 26, 1951) is an American Theoretical physicist and Professor at the Institute for Advanced Study ^[3] According to this hypothesis, when a large enough number of quarks are collected together, the lowest energy state is one which has roughly equal numbers of up, down, and strange quarks, namely a strangelet. This stability would occur because of the Pauli exclusion principle; having three types of quarks, rather than two as in normal nuclear matter, allows more quarks to be placed in lower energy levels. The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925

Relationship with nuclei

A nucleus is a collection of a large number of up and down quarks, confined into triplets (neutrons and protons). 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 According to the strange matter hypothesis, strangelets are more stable than nuclei, so nuclei are expected to decay into strangelets. But this process may be extremely slow because there is a large energy barrier to overcome: as the weak interaction starts making a nucleus into a strangelet, the first few strange quarks form strange baryons, such as the Lambda, which are heavy. Only if many conversions occur almost simultaneously will the number of strange quarks reach the critical proportion required to achieve a lower energy state. This is very unlikely to happen, so even if the strange matter hypothesis were correct, nuclei would never be seen to decay to strangelets because their lifetime would be longer than the age of the universe.

Size

The stability of strangelets depends on their size. This is because of (a) surface tension at the interface between quark matter and vacuum (which affects small strangelets more than big ones), and (b) screening of charges, which allows small strangelets to be charged, with a neutralizing cloud of electrons/positrons around them, but requires large strangelets, like any large piece of matter, to be electrically neutral in their interior. The charge screening distance tends to be of order a few femtometers, so only the outer few femtometers of a strangelet can carry charge ^[4].

The surface tension of strange matter is unknown. If it is smaller than a critical value (a few MeV per square femtometer ^[5]) then large strangelets are unstable and will tend to fission into smaller strangelets (strange stars are still stabilized, by gravity). If it is larger than the critical value, then strangelets become more stable as they get bigger.

Natural or artificial occurrence

Although nuclei do not decay to strangelets, there are other ways to create strangelets, so if the strange matter hypothesis is correct there should be strangelets in the universe. There are at least three ways they might be created in nature:

• Cosmologically, i. e. in the early universe when the QCD confinement phase transition occurred. Quantum chromodynamics (abbreviated as QCD is a theory of the Strong interaction ( color force a Fundamental force describing the interactions of the It is possible that strangelets were created along with the neutrons and protons which form ordinary matter.
• High energy processes. The universe is full of very high-energy particles (cosmic rays). For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on It is possible that when these collide with each other or with neutron stars they may provide enough energy to overcome the energy barrier and create strangelets from nuclear matter.
• Cosmic ray impacts. In addition to head-on collisions of cosmic rays, ultra high energy cosmic rays impacting Earth's atmosphere may create strangelets. In high-energy physics, an ultra-high-energy cosmic ray ( UHECR) or extreme-energy cosmic ray ( EECR) is a Cosmic ray (subatomic particle Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five

These scenarios offer possibilities for observing strangelets. If there are strangelets flying around the universe, then occasionally a strangelet should hit Earth, where it would appear as an exotic type of cosmic ray. If strangelets can be produced in high energy collisions, then we might make them at heavy-ion colliders.

Accelerator production

At heavy ion accelerators like RHIC, nuclei are collided at relativistic speeds, creating strange and antistrange quarks which could conceivably lead to strangelet production. The Relativistic Heavy Ion Collider (RHIC pronounced like " Rick " ˈrɪk is a heavy- Ion Collider located at and operated by Brookhaven The experimental signature of a strangelet would be its very high ratio of mass to charge, which would cause its trajectory in a magnetic field to be extremely straight. The STAR collaboration has searched for strangelets produced at the Relativistic Heavy Ion Collider,^[6] and none were found. The STAR detector, which stands for Solenoidal Tracker at RHIC is one of the four experiments at the Relativistic Heavy Ion Collider (RHIC in Brookhaven National The Relativistic Heavy Ion Collider (RHIC pronounced like " Rick " ˈrɪk is a heavy- Ion Collider located at and operated by Brookhaven It is believed that the higher energy of the lead-lead collisions of the Large Hadron Collider (LHC), compared to the RHIC, will produce more strange quarks in the quark-gluon plasma (QGP) than are produced at RHIC's QGP. A quark-gluon plasma (QGP is a phase of Quantum chromodynamics (QCD which exists at extremely high Temperature and/or Density. This higher production of strange quarks might allow for production of a strangelet at the LHC, and searches^[7] are planned for such upon commencement of collisions at the LHC ALICE detector. ALICE ( A Large Ion Collider Experiment) is one of the six detector experiments being constructed at the Large Hadron Collider at CERN.

Space-based detection

The Alpha Magnetic Spectrometer (AMS), an instrument which is planned to be mounted on the International Space Station, could detect strangelets ^[8].

Possible seismic detection

In May 2002, a group of researchers at Southern Methodist University reported the possibility that strangelets may have been responsible for a seismic event recorded on October 22 and November 24 in 1993 ^[9]. See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. Southern Methodist University ("SMU" is a private, Coeducational University in University Park, Texas (an enclave Events 202 BC - Hannibal Barca, leader of the Carthaginians, is defeated by the Roman legions under Scipio Africanus Events 380 - Theodosius I makes his adventus, or formal Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar) The authors later retracted their claim, after finding that the clock of one of the seismic stations had a large error during the relevant period. ^[10]

It has been suggested that the International Monitoring System being set up to verify the Comprehensive Nuclear Test Ban Treaty (CTBT) may be useful as a sort of "strangelet observatory" using the entire Earth as its detector. The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO is an International organization that will be established upon the entry into force of the Comprehensive Nuclear The Comprehensive Nuclear-Test-Ban Treaty (CTBT bans all nuclear explosions in all environments for military or civilian purposes The IMS will be designed to detect anomalous seismic disturbances down to 1 kiloton of TNT's equivalent energy release or less, and could be able to track strangelets passing through Earth in real time if properly exploited.

Dangers

If the strange matter hypothesis is correct, and a strangelet comes in contact with a lump of ordinary matter such as Earth, it could convert the ordinary matter to strange matter. This "ice-nine" disaster scenario is as follows: one strangelet hits a nucleus, catalyzing its immediate conversion to strange matter. Ice-nine is a Fictional material conceived by writer Kurt Vonnegut in his novel Cat's Cradle. This liberates energy, producing a larger, more stable strangelet, which in turn hits another nucleus, catalyzing its conversion to strange matter. In the end, all the nuclei of all the atoms of Earth are converted, and Earth is reduced to a hot, large lump of strange matter.

This is not a concern for strangelets in cosmic rays, because they are produced far from Earth and have had time to decay to their ground state, which is predicted by most (though not all ^[11]) models to be positively charged, so they are electrostatically repelled by nuclei, and would rarely merge with them ^[12][13]. But high-energy collisions could produce negatively charged strangelet states which live long enough to interact with the nuclei of ordinary matter ^[14].

The danger of catalyzed conversion by strangelets produced in heavy-ion colliders has received some media attention,^[15][16] and concerns of this type were raised ^[17][18] at the commencement of the Relativistic Heavy Ion Collider (RHIC) experiment at Brookhaven, which could potentially have created strangelets. The Relativistic Heavy Ion Collider (RHIC pronounced like " Rick " ˈrɪk is a heavy- Ion Collider located at and operated by Brookhaven A detailed analysis ^[19] concluded that the RHIC collisions were comparable to ones which naturally occur as cosmic rays traverse the solar system, so we would already have seen such a disaster if it were possible. RHIC has been operating since 2000 without incident. Similar concerns have been raised about the operation of the Large Hadron Collider (LHC) at CERN ^[20] but such fears are dismissed as far-fetched by scientists ^{[20][21] [22]}. The European Organization for Nuclear Research (Organisation Européenne pour la Recherche Nucléaire known as CERN

In the case of a neutron star, the conversion scenario seems much more plausible. 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 A neutron star is in a sense a giant nucleus (20 km across), held together by gravity, but it is electrically neutral and so does not electrostatically repel strangelets. If a strangelet hit a neutron star, it could convert a small region of it, and that region would grow to consume the entire star, creating a quark star. A quark star or strange star is a hypothetical type of Exotic star composed of Quark matter, or Strange matter. ^[23]

It should be remembered all the issues discussed above relating to the conversion of ordinary matter to strange matter only arise if the strange matter hypothesis is true, and its surface tension is larger than the afore-mentioned critical value.

Debate about the strange matter hypothesis

The strange matter hypothesis is generally regarded as a radical idea. No direct search for strangelets in cosmic rays or particle accelerators has seen a strangelet (see references in earlier sections). If any of the objects we call neutron stars could be shown to have a surface made of strange matter, this would indicate that strange matter is stable at zero pressure, which would vindicate the strange matter hypothesis. But there is no strong evidence for strange matter surfaces on neutron stars (see below).

Another argument against the hypothesis is that if it were true, all neutron stars should be made of strange matter, and otherwise none should be. ^[24] Even if there were only a few strange stars initially, violent events such as collisions would soon create many strangelets flying around the universe. Because one strangelet will convert a neutron star to strange matter, by now all neutron stars would have been converted. This argument is still debated,^{[25][26][27][28]} but if it is correct then showing that one neutron star has a conventional nuclear matter crust would disprove the strange matter hypothesis.

Because of its importance for the strange matter hypothesis, there is an ongoing effort to determine whether the surfaces of neutron stars are made of strange matter or nuclear matter. The evidence currently favors nuclear matter. This comes from the phenomenology of X-ray bursts, which is well-explained in terms of a nuclear matter crust,^[29] and from measurement of seismic vibrations in magnetars. X-ray bursters are a class of binary stars which have periodic outbursts luminous in X-rays. A magnetar is a Neutron star with an extremely powerful Magnetic field, the decay of which powers the emission of copious amounts of high-energy Electromagnetic ^[30]

In fiction

An episode of Odyssey 5 featured an attempt to destroy the planet by intentionally creating strangelets in a particle accelerator. Odyssey 5 is a Canadian Science fiction series that first ran in 2002 on Showtime in the United States and on Space

The BBC docudrama End Day features a scenario where a particle accelerator in New York City explodes, starting a catastrophic chain reaction which destroys Earth. A Docudrama is a Dramatization of actual historical events Generalities Docudramas tend to demonstrate some or most of the following characteristics End Day is a 2005 Docu-drama produced by the BBC and aired on the National Geographic Channel, on the TV series National The City of New York

References

External links and further reading

• The Story of Strangelets
• F. Weber, "Strange quark matter and compact stars", Prog. Part. Nucl. Phys. 54:193-288 (2005) arXiv:astro-ph/0407155
• J. Madsen, "Physics and Astrophysics of Strange Quark Matter" Lect. Notes Phys. 516 162-203 (1999) arXiv:astro-ph/9809032

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