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

TL;DR

The paper evaluates whether Earth-like planets can maintain surface liquid water and atmospheric retention around massive stars by integrating time-dependent HZ boundaries from GENEC stellar tracks with climate limits and XUV/wind erosion constraints. It uncovers a main-sequence mass ceiling near $\sim10\,M_\odot$, where habitable annuli exist for tens of Myr at ~tens to hundreds of AU but rapidly disappear for higher masses; post-main-sequence habitability can briefly reappear at even higher masses but only at very large separations and short durations. By incorporating two planet-multiplicity models and folding the results with Milky-Way initial mass functions, the study finds that massive stars contribute only about $f_{\ge 8}\sim(5$–$8)\times10^{-5}$ to the IMF-weighted habitability yield, i.e., a negligible fraction of the Galaxy’s Earth-analogue planet-time budget, though the absolute number of such targets remains non-zero. The work highlights the observational implications, showing that transit and direct-imaging methods face severe challenges for these distant, long-period HZs, while MIR interferometry and long-baseline surveys may still probe these systems as short-lived, distinctive biosignature targets.

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.

Figures (6)

• Figure 1: Time evolution of habitable-zone radii for six rotating solar-metallicity GENEC tracks ($0.8$, $1$, $5$, $9$, $15$, and $25\,M_\odot$; model identifiers are shown in the upper-left of each panel). The climate-only inner and outer boundaries are $r_{\rm in,clim}$ (green dashed) and $r_{\rm out,clim}$ (orange), while the adopted inner edge is $r_{\rm in}=\max(r_{\rm in,clim},\,r_{\rm wind},\,r_{\rm XUV})$ (blue); $r_{\rm wind}$ (magenta dashed) and $r_{\rm XUV}$ (purple dashed, computed for $\tau=0.1\,\mathrm{Myr}$) denote the wind- and XUV-limited constraints on atmospheric retention. The habitable band (light green shading) is defined by $r_{\rm in}<r_{\rm out,clim}$ at a given time. Vertical black lines mark the end of core-H burning (MS end).
• Figure 2: Existence time and maximum fixed-orbit residence time versus initial mass for the rotating solar-metallicity GENEC grid. Solid curves show the cumulative HZ existence durations $\Delta t_{\rm HZ}$ and dashed curves show the maximum contiguous residence time $\Delta t_{\rm res}=\max_a \Delta t(a)$, each evaluated separately on the MS and post-MS. Horizontal lines indicate benchmark residence requirements.
• Figure 3: Maximum HZ planet multiplicity inferred from Table \ref{['tab:1']}. Solid lines denote MS values and dash--dotted lines denote post-MS values. Left: Method A (geometric packing only, $K=12$) gives $N_{\rm MS}=4$ for $0.8$--$9\,M_\odot$ and a sharp collapse at higher mass, while post-MS multiplicity persists to $25\,M_\odot$. Right: Method B couples the HZ to a finite solids reservoir and shows $K=\{12,16,20\}$; it yields an MS plateau at low mass, a spike at $9\,M_\odot$, and rapid suppression once the HZ moves beyond the reservoir scale.
• Figure 4: Rotation versus non-rotation comparison of HZ boundary evolution at $9\,M_\odot$ (left) and $20\,M_\odot$ (right). Blue curves show non-rot S0 models and red curves show rot S0.4 models. Solid curves plot the operational inner edge $r_{\rm in,op}(t)$ and dashed curves plot the climate outer edge $r_{\rm out,clim}(t)$. Thin horizontal lines mark the residence-orbit locations $a_{\rm res}$ in each phase. Top panels use MS age. Bottom panels use time since TAMS. Shading marks epochs where an annulus exists, with overlap between rot and non-rot shown in purple. The annotated ratios give $t_{\rm MS,rot}/t_{\rm MS,nonrot}$ (top) and $t_{\rm post,rot}/t_{\rm post,nonrot}$ (bottom).
• Figure 5: Grid-wide rotation sensitivity of habitable time budgets and the residence orbit. Left panel shows $100\,(\Delta t_{\rm HZ,rot}-\Delta t_{\rm HZ,nonrot})/t_{\rm MS,nonrot}$ for MS and post-MS phases. Right panel shows $100\,[a_{\rm res,rot}/a_{\rm res,nonrot}-1]$ for MS and post-MS phases. Vertical dotted lines mark $M_{\rm ini}=9$ and $20\,M_\odot$, matching the detailed comparisons in Figure \ref{['fig:D1_rotation']}.