# Shell collapsar

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Hypothetical compact astrophysical object

A **shell collapsar** is a proposed alternative explanation for the observations of [black hole](/source/Black_hole) candidates. In this concept, matter collapses onto the [event horizon](/source/Event_horizon), forming a compact shell of ultra-high density. Being of neutron star size (~11km), this hypothetical object strongly [deflects](/source/Deflection_(physics)) light rays like a black hole, but has no central point-like [singularity](/source/Gravitational_singularity). The term *shell collapsar* was first proposed by [Trevor W. Marshall](https://en.wikipedia.org/w/index.php?title=Trevor_W._Marshall&action=edit&redlink=1) in 2009[1] and 2012,[2] then more firmly established in 2016.[3] It predicts the existence of [neutron star](/source/Neutron_star) masses beyond the [Tolman–Oppenheimer–Volkoff limit](/source/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit) of 2.1 M☉,[4] thus providing an alternative to stellar-mass black holes for the highly compact bodies that merge to produce [gravitational wave](/source/Gravitational_wave) signals.

In 2011, Jun Ni[5] explored the theoretical framework of neutron stars within the context of [general relativity](/source/General_relativity). He discusses solutions to the field equations that do not impose a maximum mass limit on neutron stars, which challenges the conventional understanding that there is a maximum mass beyond which a neutron star would collapse into a black hole. Ni introduced a new class of neutron stars that can exist beyond this traditional limit, suggesting that these stars could have significantly higher masses than previously thought. He coined the term "超重星" (Chōjūsei) in Japanese, which translates to "supermassive star" in English, to describe these neutron stars that defy the established mass constraints. Luboš Neslušan[6] suggested such a solution with the gravitation potential minimum in the shell of the neutron star instead of the centre and references Ni. deLyra[7] shows similar models of shell-like compact gas objects. New research from Matthew R. Edwards[8] even suggest a *shell universe* model based on Ni's solutions in order to reduce the [Hubble Tension](/source/Hubble_Tension).

A shell collapsar may be [void](/source/Void_(astronomy)) inside[9] as time dilation delays indefinitely the entry of mass-particles. Marshall's solution however, predicts intense gravitational field energy there, arising from Einsteinian gravitation in the highly non-linear regime. As [time dilation](/source/Time_dilation) is extreme on the collapsar surface (just outside the event horizon), accreting neutron matter can be viewed as freezing onto the outer shell, as described in the ‘frozar’ model.[10][11] Z. Zakir conceives that outward gravitational forces arise in the interior and push inner matter into the ‘frozar’ shell.[12]

The shell collapsar is a special case of a [gravastar](/source/Gravastar). With the gravastar, an exotic form of matter stabilizes the object with the equation of state of dark energy inside. The shell collapsar comes to a similar result with ordinary neutron star matter and simply [Einstein's field equations](/source/Einstein's_field_equations) describing intense gravitational energy density, comparable as E/c² to the neutron matter density.

## References

1. **[^](#cite_ref-1)** Marshall, T.W. (2009). "The gravitational collapse of a dust ball". [arXiv](/source/ArXiv_(identifier)):[0907.2339](https://arxiv.org/abs/0907.2339) [[gr-qc](https://arxiv.org/archive/gr-qc)].

1. **[^](#cite_ref-2)** Marshall, T.W. (2012). "Gravitational collapse without black holes". *Astrophysics and Space Science*. **342** (2): 329–332. [Bibcode](/source/Bibcode_(identifier)):[2012Ap&SS.342..329M](https://ui.adsabs.harvard.edu/abs/2012Ap&SS.342..329M). [doi](/source/Doi_(identifier)):[10.1007/s10509-012-1170-y](https://doi.org/10.1007%2Fs10509-012-1170-y).

1. **[^](#cite_ref-3)** Marshall, Trevor (2016). ["The Shell Collapsar—A Possible Alternative to Black Holes"](https://doi.org/10.3390%2Fe18100363). *Entropy*. **18** (10): 363. [Bibcode](/source/Bibcode_(identifier)):[2016Entrp..18..363M](https://ui.adsabs.harvard.edu/abs/2016Entrp..18..363M). [doi](/source/Doi_(identifier)):[10.3390/e18100363](https://doi.org/10.3390%2Fe18100363).

1. **[^](#cite_ref-4)** Marshall, Trevor. ["Neutron stars beyond the TOV limit"](https://www.researchgate.net/publication/324984059). Retrieved 2019-12-21.

1. **[^](#cite_ref-5)** Ni, Jun (July 2011). ["Solutions without a maximum mass limit of the general relativistic field equations for neutron stars"](http://link.springer.com/10.1007/s11433-011-4350-9). *Science China Physics, Mechanics and Astronomy*. **54** (7): 1304–1308. [arXiv](/source/ArXiv_(identifier)):[1103.1927](https://arxiv.org/abs/1103.1927). [Bibcode](/source/Bibcode_(identifier)):[2011SCPMA..54.1304N](https://ui.adsabs.harvard.edu/abs/2011SCPMA..54.1304N). [doi](/source/Doi_(identifier)):[10.1007/s11433-011-4350-9](https://doi.org/10.1007%2Fs11433-011-4350-9). [ISSN](/source/ISSN_(identifier)) [1674-7348](https://search.worldcat.org/issn/1674-7348).

1. **[^](#cite_ref-6)** Neslušan, L. (2024-08-01). ["Outward oriented gravitational attraction in the innermost part of the compact objects - a new feature of relativistic gravity"](https://doi.org/10.31577%2Fcaosp.2024.54.3.49). *Contributions of the Astronomical Observatory Skalnaté Pleso*. **54** (3): 49. [Bibcode](/source/Bibcode_(identifier)):[2024CoSka..54c..49N](https://ui.adsabs.harvard.edu/abs/2024CoSka..54c..49N). [doi](/source/Doi_(identifier)):[10.31577/caosp.2024.54.3.49](https://doi.org/10.31577%2Fcaosp.2024.54.3.49). [ISSN](/source/ISSN_(identifier)) [1335-1842](https://search.worldcat.org/issn/1335-1842).

1. **[^](#cite_ref-7)** deLyra, Jorge L.; de A. Orselli, Rodrigo; Carneiro, C. E. I. (May 2023). ["Exact solution of the Einstein field equations for a spherical shell of fluid matter"](https://doi.org/10.1007/s10714-023-03116-5). *General Relativity and Gravitation*. **55** (5): 68. [arXiv](/source/ArXiv_(identifier)):[2101.02012](https://arxiv.org/abs/2101.02012). [Bibcode](/source/Bibcode_(identifier)):[2023GReGr..55...68D](https://ui.adsabs.harvard.edu/abs/2023GReGr..55...68D). [doi](/source/Doi_(identifier)):[10.1007/s10714-023-03116-5](https://doi.org/10.1007%2Fs10714-023-03116-5). [ISSN](/source/ISSN_(identifier)) [0001-7701](https://search.worldcat.org/issn/0001-7701).

1. **[^](#cite_ref-8)** Edwards, Matthew R. (2024-08-07). ["Shell Universe: Reducing Cosmological Tensions with the Relativistic Ni Solutions"](https://doi.org/10.3390%2Fastronomy3030014). *Astronomy*. **3** (3): 220–239. [Bibcode](/source/Bibcode_(identifier)):[2024Astro...3..220E](https://ui.adsabs.harvard.edu/abs/2024Astro...3..220E). [doi](/source/Doi_(identifier)):[10.3390/astronomy3030014](https://doi.org/10.3390%2Fastronomy3030014). [hdl](/source/Hdl_(identifier)):[1807/139651](https://hdl.handle.net/1807%2F139651). [ISSN](/source/ISSN_(identifier)) [2674-0346](https://search.worldcat.org/issn/2674-0346).

1. **[^](#cite_ref-9)** Mitra, Abhas (2013). ["The Mass of the Oppenheimer–Snyder-Black Hole: Only Finite Mass Quasi-Black Holes"](https://www.researchgate.net/publication/239347425). *International Journal of Modern Physics D*. **22** (9): 1350054. [doi](/source/Doi_(identifier)):[10.1142/S0218271813500545](https://doi.org/10.1142%2FS0218271813500545).

1. **[^](#cite_ref-10)** Zakir, Zahid (2007). "General relativity constrains proper times and predicts frozen stars instead of black holes". *Theoretical Physics, Astrophysics and Cosmology*: 1–8. [arXiv](/source/ArXiv_(identifier)):[0705.2585](https://arxiv.org/abs/0705.2585). [doi](/source/Doi_(identifier)):[10.9751/TPAC.2497-006](https://doi.org/10.9751%2FTPAC.2497-006) (inactive 1 July 2025).{{[cite journal](https://en.wikipedia.org/wiki/Template:Cite_journal)}}: CS1 maint: DOI inactive as of July 2025 ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_DOI_inactive_as_of_July_2025))

1. **[^](#cite_ref-11)** Zakir, Zahid (2018). "On the consistency of the Oppenheimer-Snyder solution for a dust star. Reply to Marshall's criticism". *Astrophysics and Space Science*. **363** (2) 30. [Bibcode](/source/Bibcode_(identifier)):[2018Ap&SS.363...30Z](https://ui.adsabs.harvard.edu/abs/2018Ap&SS.363...30Z). [doi](/source/Doi_(identifier)):[10.1007/s10509-018-3246-9](https://doi.org/10.1007%2Fs10509-018-3246-9).

1. **[^](#cite_ref-12)** Marshall, Trevor W. ["Supermassive neutron-star mergers as source of the gravitational wave events"](https://www.researchgate.net/publication/331788250). Retrieved 2019-12-21.

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Adapted from the Wikipedia article [Shell collapsar](https://en.wikipedia.org/wiki/Shell_collapsar) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Shell_collapsar?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.