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Exotic star

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Anexotic staris a hypotheticalcompact starcomposed ofexotic matter(something not made ofelectrons,protons,neutrons,ormuons), and balanced againstgravitational collapsebydegeneracy pressureor other quantum properties.

Types of exotic stars include

Of the various types of exotic star proposed, the most well evidenced and understood is thequark star,although its existence is not confirmed.

InNewtonian mechanics,objects dense enough to trap any emitted light are calleddark stars,[1][2][a],as opposed toblack holesingeneral relativity. However, the same name is used for hypothetical ancient "stars" whichderived energy from dark matter.

Exotic stars are largely hypothetical – partly because it is difficult to test in detail how such forms of matter may behave, and partly because prior to the fledgling technology ofgravitational-wave astronomy,there was no satisfactory means of detecting compact astrophysical objects that do not radiate either electromagnetically or through known particles. While candidate objects are occasionally identified based on indirect evidence, it is not yet possible to distinguish their observational signatures from those of known objects.

Quark stars and strange stars[edit]

Main articles:Quark starandStrange star

Aquark staris a hypothesized object that results from the decomposition ofneutronsinto their constituentupanddownquarksunder gravitational pressure. It is expected to be smaller and denser than aneutron star,and may survive in this new state indefinitely, if no extra mass is added. Effectively, it is a single, very largehadron.Quark stars that containstrange matterare calledstrange stars.

Based on observations released by theChandra X-Ray Observatoryon 10 April 2002, two objects, namedRX J1856.5−3754and3C 58,were suggested as quark star candidates. The former appeared to be much smaller and the latter much colder than expected for a neutron star, suggesting that they were composed of material denser thanneutronium.However, these observations were met with skepticism by researchers who said the results were not conclusive.[who?]After further analysis, RX J1856.5−3754 was excluded from the list of quark star candidates.[3]

Electroweak stars[edit]

Main article:Electroweak star

Anelectroweak staris a hypothetical type of exotic star in which the gravitational collapse of the star is prevented byradiation pressureresulting fromelectroweak burning;that is, the energy released by the conversion ofquarksintoleptonsthrough theelectroweak force.This process occurs in a volume at the star's core approximately the size of anappleand containing about two Earth masses.[4]

The stage of life of a star that produces an electroweak star is theorized to occur after asupernovacollapse. Electroweak stars are denser than quark stars, and may form whengravitational attractioncan no longer be withstood by quarkdegeneracy pressure,but can still be withstood by electroweak-burning radiation pressure.[5] This phase of a star's life may last upwards of 10 million years.[4][5][6][7]

Preon stars[edit]

Apreon staris a proposed type of compact star made ofpreons,a group ofhypothetical subatomic particles.Preon stars would be expected to have hugedensities,exceeding 1023kg/m3.They may have greater densities than quark stars, and they would be heavier but smaller than white dwarfs and neutron stars.[8]Preon stars could originate fromsupernovaexplosions or theBig Bang.Such objects could be detected in principle throughgravitational lensingofgamma rays.Preon stars are a potential candidate fordark matter.However, current observations[9]fromparticle acceleratorsspeak against the existence of preons, or at least do not prioritize their investigation, since the only particle detector presently able to explore very high energies (theLarge Hadron Collider) is not designed specifically for this and its research program is directed towards other areas, such as studying theHiggs boson,quark–gluon plasmaand evidence related tophysics beyond the Standard Model.[clarification needed]

Boson stars[edit]

Aboson staris a hypotheticalastronomical objectformed out of particles calledbosons(conventionalstarsare formed from mostly protons and electrons, which arefermions,but also contain a large proportion ofhelium-4nuclei, which arebosons,and smaller amounts of various heavier nuclei, which can be either). For this type of star to exist, there must be a stable type of boson with self-repulsive interaction; one possible candidate particle[10] is the still-hypothetical"axion"(which is also a candidate for the not-yet-detected"non-baryonic dark matter"particles, which appear to compose roughly 25% of the mass of the Universe). It is theorized[11] that unlike normal stars (which emit radiation due to gravitational pressure and nuclear fusion), boson stars would be transparent and invisible. The immense gravity of a compact boson star would bend light around the object, creating an empty region resembling the shadow of a black hole'sevent horizon.Like a black hole, a boson star would absorb ordinary matter from its surroundings, but because of the transparency, matter (which would probably heat up and emit radiation) would be visible at its center. Simulations suggest that rotating boson stars would betorus,or "doughnut-shaped", as centrifugal forces would give the bosonic matter that form.

As of 2024,there is no significant evidence that such stars exist. However, it may become possible to detect them by the gravitational radiation emitted by a pair of co-orbiting boson stars,[12][13]andGW190521,thought to be the most energeticblack hole merging,may be the head-on collision of two boson stars.[14]

Boson stars may have formed through gravitational collapse during the primordial stages of the Big Bang.[15] At least in theory, a supermassive boson star could exist at the core of a galaxy, which may explain many of the observed properties ofactive galactic cores.[16]

Boson stars have also been proposed as candidatedark matterobjects,[17] and it has been hypothesized that thedark matter haloessurrounding mostgalaxiesmight be viewed as enormous "boson stars."[18]

The compact boson stars and boson shells are often studied involving fields like the massive (or massless)complex scalar fields,theU(1) gauge fieldand gravity withconical potential.The presence of a positive or negative cosmological constant in the theory facilitates a study of these objects inde Sitterandanti-de Sitter spaces.[19][20][21][22][23]

Boson stars composed of elementary particles with spin-1 have been labelledProca stars.[24]

Braaten, Mohapatra, and Zhang (2016) have theorized that a new type denseaxionstar may exist in which gravity is balanced by the mean-field pressure of the axionBose–Einstein condensate.[25] The possibility that dense axion stars exist has been challenged by other work that does not support this claim.[26]

Planck stars[edit]

Main article:Planck star

Inloop quantum gravity,a Planck star is a hypothetically possibleastronomical objectthat is created when theenergy densityof a collapsing star reaches thePlanck energy density.Under these conditions, assuminggravityandspacetimearequantized,there arises a repulsive "force" derived fromHeisenberg'suncertainty principle.In other words, if gravity and spacetime are quantized, the accumulation of mass-energy inside the Planck star cannot collapse beyond this limit to form agravitational singularitybecause it would violate the uncertainty principle for spacetime itself.[27]

Q-stars[edit]

Q-stars are hypothetical objects that originate fromsupernovaeor the big bang. They are theorized to be massive enough to bend space-time to a degree such that some, but not all light could escape from its surface. These are predicted to be denser thanneutron starsor even quark stars.[28]

See also[edit]

Footnotes[edit]

  1. ^ Quantum effects may prevent true black holes from forming and give rise instead to dense entities calledblack stars.[2]

References[edit]

  1. ^Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (February 2009). "Small, dark, and heavy: But is it a black hole?".arXiv:0902.0346v2[gr-qc]. Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (2009). "Small, dark, and heavy: But is it a black hole?".arXiv:0902.0346v2[gr-qc].
  2. ^ab Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (30 September 2009)."How quantum effects could create black stars, not holes".Scientific American.No. October 2009. Archived fromthe originalon 15 November 2013.Retrieved25 December2022.Originally published with title"Black Stars, Not Holes".
  3. ^ Truemper, J.E.; Burwitz, V.; Haberl, F.; Zavlin, V.E. (June 2004). "The puzzles of RX J1856.5-3754: neutron star or quark star?".Nuclear Physics B: Proceedings Supplements.132:560–565.arXiv:astro-ph/0312600.Bibcode:2004NuPhS.132..560T.doi:10.1016/j.nuclphysbps.2004.04.094.S2CID425112.
  4. ^ab Shiga, D. (4 January 2010)."Exotic stars may mimic Big Bang".New Scientist.Archivedfrom the original on 18 January 2010.Retrieved18 February2010.
  5. ^ab "Theorists propose a new way to shine – and a new kind of star: 'Electroweak'"(Press release).Case Western Reserve University.15 December 2009.Archivedfrom the original on 21 February 2020.Retrieved16 December2009– viaScienceDaily.
  6. ^ Vieru, Tudor (15 December 2009)."New type of cosmic objects: Electroweak stars".Softpedia.Archivedfrom the original on 18 December 2009.Retrieved16 December2009.
  7. ^ "Astronomers predict new class of 'electroweak' star".Technology Review.10 December 2009. Archived fromthe originalon 19 October 2012.Retrieved16 December2009.
  8. ^Hannson, J.; Sandin, F. (9 June 2005). "Preon stars: A new class of cosmic compact objects".Physics Letters B.616(1–2): 1–7.arXiv:astro-ph/0410417.Bibcode:2005PhLB..616....1H.doi:10.1016/j.physletb.2005.04.034.S2CID119063004.
  9. ^Wilkins, Alasdair (9 December 2010)."Stars so weird that they make black holes look boring".io9.Archivedfrom the original on 28 March 2014.Retrieved12 September2015.
  10. ^ Kolb, Edward W.; Tkachev, Igor I. (29 March 1993). "Axion miniclusters and Bose stars".Physical Review Letters.71(19): 3051–3054.arXiv:hep-ph/9303313.Bibcode:1993PhRvL..71.3051K.doi:10.1103/PhysRevLett.71.3051.PMID10054845.S2CID16946913.
  11. ^ Clark, Stuart (15 July 2017). "Holy moley! (Astronomers taking a first peek at our galaxy's black heart might be in for a big surprise)".New Scientist.p. 29.
  12. ^ Schutz, Bernard F. (2003).Gravity from the Ground Up(3rd ed.).Cambridge University Press.p.143.ISBN0-521-45506-5.
  13. ^ Palenzuela, C.; Lehner, L.; Liebling, S.L. (2008). "Orbital dynamics of binary boson star systems".Physical Review D.77(4): 044036.arXiv:0706.2435.Bibcode:2008PhRvD..77d4036P.doi:10.1103/PhysRevD.77.044036.S2CID115159490.
  14. ^ Bustillo, Juan Calderón; Sanchis-Gual, Nicolas; Torres-Forné, Alejandro; Font, José A.; Vajpeyi, Avi; Smith, Rory; et al. (2021)."GW190521 as a merger of Proca stars: A potential new vector Boson of 8.7×10−13eV ".Physical Review Letters.126(8): 081101.arXiv:2009.05376.doi:10.1103/PhysRevLett.126.081101.hdl:10773/31565.PMID33709746.S2CID231719224.
  15. ^ Madsen, Mark S.; Liddle, Andrew R. (1990). "The cosmological formation of boson stars".Physics Letters B.251(4): 507.Bibcode:1990PhLB..251..507M.doi:10.1016/0370-2693(90)90788-8.
  16. ^ Torres, Diego F.; Capozziello, S.; Lambiase, G. (2000). "A supermassive Boson star at the galactic center?".Physical Review D.62(10): 104012.arXiv:astro-ph/0004064.Bibcode:2000PhRvD..62j4012T.doi:10.1103/PhysRevD.62.104012.S2CID16670960.
  17. ^ Sharma, R.; Karmakar, S.; Mukherjee, S. (2008). "Boson star and dark matter".arXiv:0812.3470[gr-qc].
  18. ^ Lee, Jae-weon; Koh, In-guy (1996). "Galactic halos as Boson stars".Physical Review D.53(4): 2236–2239.arXiv:hep-ph/9507385.Bibcode:1996PhRvD..53.2236L.doi:10.1103/PhysRevD.53.2236.PMID10020213.S2CID16914311.
  19. ^ Kumar, S.; Kulshreshtha, U.; Kulshreshtha, D.S. (2016). "Charged compact boson stars and shells in the presence of a cosmological constant".Physical Review D.94(12): 125023.arXiv:1709.09449.Bibcode:2016PhRvD..94l5023K.doi:10.1103/PhysRevD.94.125023.S2CID54590086.
  20. ^ Kumar, S.; Kulshreshtha, U.; Kulshreshtha, D.S. (2016). "Charged compact boson stars and shells in the presence of a cosmological constant".Physical Review D.93(10): 101501.arXiv:1605.02925.Bibcode:2016PhRvD..93j1501K.doi:10.1103/PhysRevD.93.101501.S2CID118474697.
  21. ^ Kleihaus, B.; Kunz, J.; Lammerzahl, C.; List, M. (2010). "Boson Shells Harbouring Charged Black Holes".Physical Review D.82(10): 104050.arXiv:1007.1630.Bibcode:2010PhRvD..82j4050K.doi:10.1103/PhysRevD.82.104050.S2CID119266501.
  22. ^ Hartmann, B.; Kleihaus, B.; Kunz, J.; Schaffer, I. (2013). "Compact (A)dS Boson stars and shells".Physical Review D.88(12): 124033.arXiv:1310.3632.Bibcode:2013PhRvD..88l4033H.doi:10.1103/PhysRevD.88.124033.S2CID118721877.
  23. ^ Kumar, S.; Kulshreshtha, U.; Kulshreshtha, D.S.; Kahlen, S.; Kunz, J. (2017). "Some new results on charged compact boson stars".Physics Letters B.772:615–620.arXiv:1709.09445.Bibcode:2017PhLB..772..615K.doi:10.1016/j.physletb.2017.07.041.S2CID119375441.
  24. ^ Brito, Richard; Cardoso, Vitor; Herdeiro, Carlos A.R.; Radu, Eugen (January 2016)."Proca stars: Gravitating Bose–Einstein condensates of massive spin 1 particles".Physics Letters B.752:291–295.arXiv:1508.05395.Bibcode:2016PhLB..752..291B.doi:10.1016/j.physletb.2015.11.051.hdl:11573/1284757.S2CID119110645.Archivedfrom the original on 25 November 2021.Retrieved25 July2021.
  25. ^ Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong (2016)."Dense axion stars".Physical Review Letters.117(12): 121801.arXiv:1512.00108.Bibcode:2016PhRvL.117l1801B.doi:10.1103/PhysRevLett.117.121801.PMID27689265.S2CID34997021.Archivedfrom the original on 28 April 2020.Retrieved26 September2018.
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Sources[edit]

External links[edit]

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