This article is about the hypothetical particle. For the album, seeStrangelet (album).
Astrangelet (pronounced/ˈstreɪndʒ.lɪt/) is ahypothetical particle consisting of abound state of roughly equal numbers ofup,down, andstrangequarks. An equivalent description is that a strangelet is a small fragment ofstrange matter, small enough to be considered aparticle. The size of an object composed of strange matter could, theoretically, range from a fewfemtometers across (with the mass of a light nucleus) to arbitrarily large. Once the size becomes macroscopic (on the order of metres across), such an object is usually called astrange star. The term "strangelet" originates withEdward Farhi andRobert Jaffe in 1984. It has been theorized that strangelets can convert matter to strange matter on contact.[1] Strangelets have also been suggested as adark matter candidate.[2]
The known particles with strange quarks are unstable. Because the strange quark is heavier than the up and down quarks, it canspontaneously decay, via theweak interaction, into an up quark. Consequently, particles containing strange quarks, such as thelambda particle, always lose theirstrangeness, by decaying into lighter particles containing only up and down quarks.
However, condensed states with a larger number of quarks might not suffer from this instability. That possible stability against decay is the "strange matter hypothesis", proposed separately byArnold Bodmer[3] andEdward Witten.[4] According to this hypothesis, when a large enough number of quarks are concentrated 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 thePauli 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.
A nucleus is a collection of a number of up and down quarks (in some nuclei a fairly large number), confined into triplets (neutrons andprotons). 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.[5]
The stability of strangelets depends on their size, because of
surface tension at the interface between quark matter and vacuum (which affects small strangelets more than big ones). The surface tension of strange matter is unknown. If it is smaller than a critical value (a few MeV per square femtometer[6]) then large strangelets are unstable and will tend to fission into smaller strangelets (strange stars would still be stabilized by gravity). If it is larger than the critical value, then strangelets become more stable as they get bigger.
screening[clarification needed] 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 the order of a few femtometers, so only the outer few femtometers of a strangelet can carry charge.[7]
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:
Cosmogonically, i.e. in the early universe when theQCD confinement phase transition occurred. It is possible that strangelets were created along with the neutrons and protons that form ordinary matter.
High-energy processes. The universe is full of very high-energy particles (cosmic rays). 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. Some identified exotic cosmic ray events, such as "Price's event"—i.e., those with very low charge-to-mass ratios (as thes-quark itself possesses charge commensurate with the more-familiard-quark, but is much more massive)—could have already registered strangelets.[8][9]
These scenarios offer possibilities for observing strangelets. If strangelets can be produced in high-energy collisions, then they might be produced by heavy-ion colliders. Similarly, if there are strangelets flying around the universe, then occasionally a strangelet should hit Earth, where it may appear as an exotic type of cosmic ray; alternatively, a stable strangelet could end up incorporated into the bulk of the Earth's matter, acquiring an electron shell proportional to its charge and hence appearing as an anomalously heavy isotope of the appropriate element—though searches for such anomalous "isotopes" have, so far, been unsuccessful.[10]
At heavy ion accelerators like theRelativistic Heavy Ion Collider (RHIC), nuclei are collided at relativistic speeds, creating strange and antistrange quarks that could conceivably lead to strangelet production. 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 very nearly, but not quite, straight. TheSTAR collaboration has searched for strangelets produced at the RHIC,[11] but none were found. TheLarge Hadron Collider (LHC) is even less likely to produce strangelets,[12] but searches are planned[13] for the LHCALICE detector.
In May 2002, a group of researchers atSouthern Methodist University reported the possibility that strangelets may have been responsible for seismic events recorded on October 22 and November 24 in 1993.[15] 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.[16]
It has been suggested that theInternational Monitoring System be set up to verify theComprehensive Nuclear Test Ban Treaty (CTBT) after entry into force may be useful as a sort of "strangelet observatory" using the entire Earth as its detector. The IMS will be designed to detect anomalous seismic disturbances down to 1kiloton of TNT (4.2 TJ) energy release or less, and could be able to track strangelets passing through Earth in real time if properly exploited.
It has been suggested that strangelets of subplanetary (i.e. heavy meteorite) mass would puncture planets and other Solar System objects, leading to impact craters which show characteristic features.[17]
If the strange matter hypothesis is correct, and if a stable negatively-charged strangelet with a surface tension larger than the aforementioned critical value exists, then a larger strangelet would be more stable than a smaller one. One speculation that has resulted from the idea is that a strangelet coming into contact with a lump of ordinary matter could over time convert the ordinary matter to strange matter.[18][19]
This is not a concern for strangelets incosmic rays because they are produced far from Earth and have had time to decay to theirground state, which is predicted by most models to be positively charged, so they areelectrostatically repelled by nuclei, and would rarely merge with them.[20][21] On the other hand, high-energy collisions could produce negatively charged strangelet states, which could live long enough to interact with the nuclei ofordinary matter.[22]
The danger of catalyzed conversion by strangelets produced inheavy-ion colliders has received some media attention,[23][24] and concerns of this type were raised[18][25] at the commencement of theRHIC experiment atBrookhaven, which could potentially have created strangelets. A detailed analysis[19] concluded that the RHIC collisions were comparable to ones which naturally occur as cosmic rays traverse theSolar 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 theLHC atCERN[26] but such fears are dismissed as far-fetched by scientists.[26][27][28]
In the case of aneutron star, the conversion scenario may be more plausible. A neutron star is in a sense a giant nucleus (20 km across), held together bygravity, but it is electrically neutral and would not electrostatically repel strangelets. If a strangelet hit a neutron star, it might catalyze quarks near its surface to form into more strange matter, potentially continuing until the entire star became astrange star.[29]
The strange matter hypothesis remains unproven. No direct search for strangelets in cosmic rays orparticle accelerators has yet confirmed a strangelet. If any of the objects such as neutron stars could be shown to have a surface made of strange matter, this would indicate that strange matter is stable at zeropressure, which would vindicate the strange matter hypothesis. However, there is no strong evidence for strange matter surfaces on neutron stars.
Another argument against the hypothesis is that if it were true, essentially all neutron stars should be made of strange matter, and otherwise none should be.[30] Even if there were only a few strange stars initially, violent events such as collisions would soon create many fragments of strange matter flying around the universe. Because collision with a single strangelet would convert a neutron star to strange matter, all but a few of the most recently formed neutron stars should by now have already been converted to strange matter.
This argument is still debated,[31][32][33][34] but if it is correct then showing that one old 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 ornuclear matter. The evidence currently favors nuclear matter. This comes from thephenomenology ofX-ray bursts, which is well explained in terms of a nuclear matter crust,[35] and from measurement of seismic vibrations inmagnetars.[36]
An episode ofOdyssey 5 featured an attempt to destroy the planet by intentionally creating negatively charged strangelets in aparticle accelerator.[37]
TheBBCdocudramaEnd Day features a scenario where a particle accelerator inNew York City explodes, creating a strangelet and starting a catastrophic chain reaction which destroys Earth.
Impact, published in 2010 and written byDouglas Preston, deals with an alien machine that creates strangelets. The machine's strangelets impact the Earth and Moon and pass through.
The novelPhobos, published in 2011 and written bySteve Alten as the third and final part of hisDomain trilogy, presents a fictional story where strangelets are unintentionally created at theLHC and escape from it to destroy the Earth.
In the 1992 black-comedy novelHumans byDonald E. Westlake, an irritated God sends an angel to Earth to bring aboutArmageddon by means of using a strangelet created in a particle accelerator to convert the Earth into a quark star.
In the 2010 filmQuantum Apocalypse, a strangelet approaches the Earth from space.
In the novelThe Quantum Thief byHannu Rajaniemi and the rest of the trilogy, strangelets are mostly used as weapons, but during an early project toterraform Mars, one was used to convertPhobos into an additional "sun".
^Rybczynski, M.; Wlodarczyk, Z.; Wilk, G. (2002). "Can cosmic rays provide sign of strangelets?".Acta Physica Polonia B.33 (1):277–296.arXiv:hep-ph/0109225.Bibcode:2002AcPPB..33..277R.
^Abelev, B. I.; Aggarwal, M. M.; Ahammed, Z.; Anderson, B. D.; Arkhipkin, D.; Averichev, G. S.; Bai, Y.; Balewski, J.; Barannikova, O.; Barnby, L. S.; Baudot, J.; Baumgart, S.; Belaga, V. V.; Bellingeri-Laurikainen, A.; Bellwied, R.; Benedosso, F.; Betts, R. R.; Bhardwaj, S.; Bhasin, A.; Bhati, A. K.; Bichsel, H.; Bielcik, J.; Bielcikova, J.; Bland, L. C.; Blyth, S. -L.; Bombara, M.; Bonner, B. E.; Botje, M.; Bouchet, J.; et al. (2007). "Strangelet search in Au+Au collisions at sNN=200 GeV".Physical Review C.76 (1): 011901.arXiv:nucl-ex/0511047.Bibcode:2007PhRvC..76a1901A.doi:10.1103/PhysRevC.76.011901.S2CID119498771.
^Sadovsky, S. A.; Kharlov, Yu. V.; Angelis, A. L. S.; Gładysz-Dziaduš, E.; Korotkikh, V. L.; Mavromanolakis, G.; Panagiotou, A. D. (2004). "Model for describing the production of Centauro events and strangelets in heavy-ion collisions".Physics of Atomic Nuclei.67 (2):396–405.arXiv:nucl-th/0301003.Bibcode:2004PAN....67..396S.doi:10.1134/1.1648929.S2CID117706766.
^Sandweiss, J. (2004). "Overview of strangelet searches and Alpha Magnetic Spectrometer: When will we stop searching?".Journal of Physics G: Nuclear and Particle Physics.30 (1):S51 –S59.Bibcode:2004JPhG...30S..51S.doi:10.1088/0954-3899/30/1/004.
^Anderson, D. P.; Rajagopal, Krishna; Reddy, Sanjay; Steiner, Andrew (2003). "Unexplained Sets of Seismographic Station Reports and a Set Consistent with a Quark Nugget Passage".The Bulletin of the Seismological Society of America.93 (6):2363–2374.arXiv:astro-ph/0205089.Bibcode:2003BuSSA..93.2363A.doi:10.1785/0120020138.S2CID43388747.
^Heger, Alexander; Cumming, Andrew; Galloway, Duncan K.; Woosley, Stanford E. (2007). "Models of type I X-ray bursts from GS 1826-24: A probe of rp-process hydrogen burning".The Astrophysical Journal.671 (2): L141.arXiv:0711.1195.Bibcode:2007ApJ...671L.141H.doi:10.1086/525522.S2CID14986572.
