Iron star

This article is about a category of stars. For iron cores of white dwarf stars, see white dwarf § Iron core.

In astronomy, the term iron star has been used for two observed types of star:

• Binary stars with highly variable emission and stellar spectral type Fe.
• a blue supergiant with a forest of forbidden Fe_II lines in its spectrum.

XX Oph and AS 352

The term iron star was applied to a star called "XX Oph" or "Merrill's Iron Star" with a complex, highly variable spectrum with a forest of Fe II emission lines. First discovered in 1908 by Williamina Fleming, it was studied over 30 years by Paul W. Merrill. The star is believed to be a non-eclipsing binary star. ^[1]

A second binary star, AS 325, has a similar spectrum and complex spectral variability and has been characterized as the second iron star. ^[2]

Blue supergiant

Other sources characterize an iron star as a type of blue supergiant which has a forest of forbidden Fe_II lines in its spectrum. They are potentially quiescent hot luminous blue variables. Eta Carinae has been described as a prototypical example. ^{[3] [4]}

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.^{[ citation needed ]}

• In the Wrath of the Gods (mod) add-on for the Calamity Mod (a mod for the video game Terraria ), the Avatar of Emptiness boss utilizes an attack where it summons and compresses an iron star to the point of it cracking, causing beams of energy to discharge from the fissures toward the player. The continued compression causes the iron star to eventually explode into damaging debris.^{[ citation needed ]}

See also

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

References

1. Howell, Steve B.; Kalari, Venu M.; Adamson, Andy; Everett, Mark (July 1, 2025). "Inside the Iron Curtain: A Long Term Look at the Iron Stars XX Oph and AS 325". Publications of the Astronomical Society of the Pacific. 137 (7): 074205. doi:10.1088/1538-3873/adeec6. ISSN   0004-6280.
2. Bopp, Bernard W.; Howell, Steve B. (November 1989). "AS 325 - Another 'iron star'?". Publications of the Astronomical Society of the Pacific. 101: 981. doi:10.1086/132562. ISSN   0004-6280.
3. 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 .
4. 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 & Astrophysics. 541: A146. arXiv: 1202.4409 . Bibcode:2012A&A...541A.146C. doi:10.1051/0004-6361/201118440. S2CID   17900583.