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.
|Event type||Formation of a hypothetical type of compact star|
|Date||c. 101500 years from now|
|Duration||c. 101026 to 101076 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|
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. 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.