Strange star

A strange star is a quark star made of strange quark matter. They form a subgroup under the quark star category.[1][2][3]

Strange stars might exist without regard to the Bodmer–Witten assumption of stability at near-zero temperatures and pressures, as strange quark matter might form and remain stable at the core of neutron stars, in the same way as ordinary quark matter could.[4] Such strange stars will naturally have a crust layer of neutron star material. The depth of the crust layer will depend on the physical conditions and circumstances of the entire star and on the properties of strange quark matter in general.[5] Stars partially made up of quark matter (including strange quark matter) are also referred to as hybrid stars.[6][7][8][9]

This theoretical strange star crust is proposed to be a possible reason behind fast radio bursts (FRBs). This is still theoretical, but there is good evidence[6][7][8][9] that the collapse of these strange star crusts may be an FRB point of origin.

Characteristics

Recent theoretical research has found the mechanisms by which the quark stars with "strange quark nuggets"[10] may decrease the objects' electric fields and the densities from previous theoretical expectations, causing such stars to appear nearly indistinguishable from ordinary neutron stars. This suggests that many, or even all, known neutron stars might be the strange stars. However, the investigating team of Jaikumar, Reddy, and Steiner (2006)[10] made some fundamental assumptions that led to uncertainties in their results significant enough that the question is not settled. More research, both observational and theoretical, remains to be done on strange stars in the future.[10]

Other theoretical work contends that :

A sharp interface between quark matter and the vacuum would have very different properties from the surface of a neutron star.[11]

Addressing key parameters like surface tension and electrical forces that were neglected in the original study, the results show that as long as the surface tension is below a low critical value, the large strangelets are indeed unstable to fragmentation and strange stars naturally come with complex strangelet crusts, analogous to those of neutron stars.[11]
Crust collapse

For a strange star's crust to collapse, it must accrete matter from its environment in some form.

The release of even small amounts of its matter causes a cascading effect on the star's crust. This is thought to result in a massive release of magnetic energy as well as electron and positron pairs in the initial phases of the collapsing stage. This release of high energy particles and magnetic energy in such a short period of time causes the newly released electron / positron pairs to be directed towards the poles of the strange star due to the increased magnetic energy created by the initial secretion of the strange star's matter. Once these electron / positron pairs are directed to the star's poles, they are then ejected at relativistic velocities, which is proposed to be one of the causes of FRBs.
Primordial strange stars

Theoretical investigations have revealed that quark stars might not only be produced from neutron stars and powerful supernovae, they could also be created in the early cosmic phase separations following the Big Bang.[12]

If these primordial quark stars can transform into strange quark matter before the external temperature and pressure conditions of the early universe renders them unstable, they might become stable, if the Bodmer–Witten assumption holds true. Such primordial strange stars could survive to this day.[12]
References

Alcock, Charles; Farhi, Edward; Olinto, Angela (1986). "Strange stars". Astrophys. J. 310: 261–272. Bibcode:1986ApJ...310..261A. doi:10.1086/164679.
P., Haensel; R., Schaeffer; J.L., Zdunik (1986). "Strange quark stars". Astronomy and Astrophysics. 160.
Weber, Fridolin; et al. (1994). Strange-matter Stars. Proceedings: Strangeness and Quark Matter. World Scientific. Bibcode:1994sqm..symp....1W.
Stuart L. Shapiro; Saul A. Teukolsky (20 November 2008). Black Holes, White Dwarfs, and Neutron Stars: The Physics of Compact Objects. John Wiley & Sons. pp. 2ff. ISBN 978-3-527-61767-8.
Kodama Takeshi; Chung Kai Cheong; Duarte Sergio Jose Barbosa (1 March 1990). Relativistic Aspects Of Nuclear Physics - Rio De Janeiro International Workshop. #N/A. pp. 241–. ISBN 978-981-4611-69-5.
Alford, Mark G.; Han, Sophia; Prakash, Madappa (2013). "Generic conditions for stable hybrid stars". Physical Review D. 88 (8): 083013.arXiv:1302.4732. Bibcode:2013PhRvD..88h3013A. doi:10.1103/PhysRevD.88.083013. S2CID 118570745.
Goyal, Ashok (2004). "Hybrid stars". Pramana. 62 (3): 753–756.arXiv:hep-ph/0303180. Bibcode:2004Prama..62..753G. doi:10.1007/BF02705363. S2CID 16582500.
Benić, Sanjin; Blaschke, David; Alvarez-Castillo, David E; Fischer, Tobias; Typel, Stefan (2015). "A new quark-hadron hybrid equation of state for astrophysics". Astronomy & Astrophysics. 577: A40.arXiv:1411.2856. Bibcode:2015A&A...577A..40B. doi:10.1051/0004-6361/201425318. S2CID 55228960.
Alvarez-Castillo, D; Benic, S; Blaschke, D; Han, Sophia; Typel, S (2016). "Neutron star mass limit at 2 M⊙ supports the existence of a CEP". The European Physical Journal A. 52 (8): 232.arXiv:1608.02425. Bibcode:2016EPJA...52..232A. doi:10.1140/epja/i2016-16232-9. S2CID 119207674.
Jaikumar, P.; Reddy, S.; Steiner, A. W. (2006). "Strange star surface: A crust with nuggets". Physical Review Letters. 96 (4): 041101.arXiv:nucl-th/0507055. Bibcode:2006PhRvL..96d1101J. doi:10.1103/PhysRevLett.96.041101. PMID 16486800. S2CID 7884769.
Alford, Mark G.; Rajagopal, Krishna; Reddy, Sanjay; Steiner, Andrew W. (2006). "Stability of strange star crusts and strangelets". Physical Review D. 73 (11): 114016.arXiv:hep-ph/0604134. Bibcode:2006PhRvD..73k4016A. doi:10.1103/PhysRevD.73.114016. S2CID 35951483.

Witten, Edward (1984). "Cosmic separation of phases". Physical Review D. 30 (2): 272–285. Bibcode:1984PhRvD..30..272W. doi:10.1103/PhysRevD.30.272.