Astrange star, also called astrange quark star,^[1]: 352 is a hypothetical compact astronomical object, aquark star made ofstrange quark matter.^[2][3][4]

Strange stars might exist without regard to theBodmer–Witten assumption of stability at near-zero temperatures and pressures, as strange quark matter might form and remain stable at the core ofneutron stars, in the same way as ordinary quark matter could.^[5] Such strange stars will naturally have a crust layer ofneutron matter. 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.^[6] Stars partially made up of quark matter (including strange quark matter) are also referred to ashybrid stars.^{[7][8][9][10]}

The collapse of the crust layer of strange stars is one of the proposed causes offast radio bursts.^{[7][8][9][10]}

Neutron stars are formed when the collapse of a star occurs with such intense force that gravity forcessubatomic particles such asprotons andelectrons to merge into neutrally chargedneutron particles, releasing a shower ofneutrinos. If the resultant neutral core is able to maintain form and not collapse into ablack hole, the result is an incredibly dense celestial body composed almost entirely of uncharged particles.

Protons and neutrons are composed of threequarks: a proton by twoup quarks and onedown quark, a neutron by two down quarks and one up quark. It is hypothesized that within neutron stars, the conditions are so extreme that a process known asdeconfinement occurs: where subatomic particles dissolve and leave their constituent quarks behind as free particles. The temperature and pressure would then force these quarks to be squeezed together to such an extent that they would form a hypotheticalphase of matter known asquark matter. If this occurs, the neutron star becomes a "quark star". If the pressure is great enough, the quarks could be affected even further and a portion could transform intostrange quarks, which would then interact with the other "non-strange" quarks to formstrange matter. If this occurs, the quark star would then become a strange star.

Early work on strange quark matter suggested that it would be a homogeneous liquid, but other models propose^[11] a heterogeneous alternative with positively charged "strange quark nuggets" embedded in a negatively charged electron gas.^[1] This structure decreases the stars' external electric field and density variation from previous theoretical expectations, with the result that such stars appear nearly indistinguishable from ordinary neutron stars.

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.^[12]

Addressing key parameters likesurface tension andelectrical 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 largestrangelets are indeed unstable to fragmentation and strange stars naturally come with complex strangelet crusts, analogous to those of neutron stars.^[12]

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.^[13] This is thought to result in a massive release of magnetic energy as well as electron-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 offast radio bursts.

Theoretical investigations have revealed that quark stars might not only be produced from neutron stars and powerfulsupernovae, they could also be created in the earlycosmic phase separations following theBig Bang, similar to hypotheticalprimordial black holes.^[14]

If these primordial quark stars can transform into strange quark matter before the external temperature and pressure conditions of theearly universe renders them unstable, they might become stable, if the Bodmer–Witten assumption holds true. Such primordial strange stars could survive to this day.^[14]

Hypothetical strange-quark dwarfs would bewhite dwarf stars with strange-quark cores. Some studies predict these objects would be stable, while others predict instability.^[15] A survey examined the mass–radius relation for 40,000 white dwarfs and found eight exceptions were much smaller in size and matched predictions for a strange dwarf.^[16]

• Stellar classification
• Exotic star

• Zhang, Yue; Geng, Jin-Jun; Huang, Yong-Feng (2018)."Fast radio bursts from the collapse of strange star crusts".The Astrophysical Journal.858 (2): 88.arXiv:1805.04448.Bibcode:2018ApJ...858...88Z.doi:10.3847/1538-4357/aabaee.S2CID 119245040. – Original scientific paper source
• "Are mysterious fast radio bursts coming from the collapse of strange star crusts?". 19 May 2018. – Simpler breakdown of said scientific paper.

• Quark stars
• Hypothetical stars
• Exotic matter
• Strange quark

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