The Sun appears to be a fairly normal main-sequence star from the outside, but might it contain a small primordial black hole? If so, it would be partially powered by accretion luminosity from the microscopic black hole in its core and would follow an evolutionary path that diverges from a typical G-type dwarf. Building on previous work (E. P. Bellinger et al. Astrophys. J. 959, 113; 2023), Matthew Caplan, Earl Bellinger and Andrew Santarelli have computed two evolutionary models for such a scenario, finding that these so-called ‘Hawking stars’ eventually become sub-solar-mass black holes. One evolutionary path proceeds through a long-lived sub-subgiant phase, while in the other, the star experiences rapid direct collapse after the main sequence.

Primordial black holes are hypothetical objects that may be of almost any mass, but those in the asteroid-mass window (10^–16 – 10^–10 M_ʘ) might be captured by stars when they are forming. This mass range is also one of the few allowed by the observational constraints upon dark matter, of which primordial black holes may be a component. Depending on whether photons from accretion onto the black hole escape freely from the stellar interior, the researchers’ MESA models show that the star can form a He core surrounded by an H-burning shell (as is typical for a low-mass star) or accretion proceeds at an increasingly rapid pace until the black hole cannibalizes the star.