Habitable Zones Around Massive Stars: From the Main Sequence to Supergiants

Abstract

Massive stars dominate the radiative and mechanical feedback of young stellar populations, yet their intense ultraviolet fields and strong winds are typically presumed to preclude Earth-like habitability. We quantify this expectation by mapping time dependent habitable zones (HZs) for solar-metallicity stars with initial masses of $0.8$-$120\,M_\odot$. From rotating and non-rotating \textsc{GENEC} tracks we derive bolometric ``climate'' HZ boundaries and enforce XUV energy-limited escape and wind ram-pressure retention constraints for a dipole-magnetized Earth analogue. The operational inner edge is set by the most restrictive limit, and we measure the annulus lifetime, the longest continuous residence at fixed orbit, and the maximum number of dynamically packed terrestrial planets it can host. We find a sharp main-sequence ceiling: while a $9\,M_\odot$ star sustains an operational HZ for $\sim 30$~Myr at $\sim 70$-$130$~AU, the main-sequence annulus becomes brief and extremely narrow by $12\,M_\odot$ and disappears by $15\,M_\odot$. Post main-sequence evolution can reopen HZs up to $\sim 25$-$30\,M_\odot$, but only for $\sim 0.03$-$1.5$~Myr at hundreds to $\sim 10^3$~AU, disappearing by $\sim 40\,M_\odot$. Rotation modestly increases habitable lifetimes near the upper main sequence without altering the high mass ceiling. Initial Mass Function (IMF) weighting shows that massive stars contribute only $\sim 10^{-4}$ of the habitable planet-time budget. Even so, they still add of order a few $10^{5}$ operationally habitable Earth analogues to the Milky Way at any instant. This implies that massive star systems are unlikely to dominate the Galaxy wide habitability budget, but they may still provide a set of short-lived, observationally distinct targets for biosignature searches.