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In astronomy, an iron star is a hypothetical type of compact star.

Unrelatedly, the term "iron star" is also used for blue supergiants which have a forest of "forbidden" FeII lines in their spectra. They are potentially quiescent hot luminous blue variables. Eta Carinae has been described as a prototypical example.[1][2]

Formation of iron starsEvent type Formation of a hypothetical type of compact star
Date c. 101500 years from now
Duration c. 1010^26 to 1010^76 years from now
Epoch Extremely far future
Source Fusion occurring via quantum tunnelling causing nuclei to fuse into iron-56 nuclei
Notable features Only a possibility if protons do not decay.
Followed by Formation of neutron stars and black holes

An iron star is a hypothetical type of compact star that could occur in the universe in the extremely far future, after perhaps 101500 years.

The premise behind the formation of iron stars states that cold fusion occurring via quantum tunnelling would cause the light nuclei in ordinary matter to fuse into iron-56 nuclei. Fission and alpha-particle emission would then make heavy nuclei decay into iron, converting stellar-mass objects to cold spheres of iron.[3] The formation of these stars is only a possibility if protons do not decay. Though the surface of a neutron star may be iron according to some predictions, it is distinct from an iron star.

By the end of 1010^26 to 1010^76 years, iron stars would have collapsed into neutron stars and black holes.[3]
In popular culture

The Soviet film The Andromeda Nebula is about a starship low on fuel caught by an iron star's gravity, with the star itself being so dim that it can only be seen in the infrared. It is based on the novel Andromeda Nebula by Ivan Yefremov written when steady state theory was dominant and iron stars were expected to exist in the Milky Way.

In the episode "Iron Stars" of Civilizations at the End of Time YouTube series, Isaac Arthur discusses about the possibilities of advanced artificial civilizations living around iron stars, and beyond the last viable sources of energy.[4]

See also

Astronomy portal iconStar portal

Future of an expanding universe
Hypothetical star
Heat death of the universe


Walborn, Nolan R.; Fitzpatrick, Edward L. (2000). "The OB Zoo: A Digital Atlas of Peculiar Spectra". The Publications of the Astronomical Society of the Pacific. 112 (767): 50. Bibcode:2000PASP..112...50W. doi:10.1086/316490.
Clark, J. S.; Castro, N.; Garcia, M.; Herrero, A.; Najarro, F.; Negueruela, I.; Ritchie, B. W.; Smith, K. T. (2012). "On the nature of candidate luminous blue variables in M 33". Astronomy and Astrophysics. 541: A146. arXiv:1202.4409. Bibcode:2012A&A...541A.146C. doi:10.1051/0004-6361/201118440. S2CID 17900583.
Dyson, Freeman J. (1979). "Time without end: Physics and biology in an open universe". Reviews of Modern Physics. 51 (3): 447–460. Bibcode:1979RvMP...51..447D. doi:10.1103/RevModPhys.51.447.

Arthur, Isaac (13 July 2017). Civilizations at the End of Time: Iron Stars. YouTube. Retrieved 9 November 2020.



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Substellar object
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