On the maximum black hole mass at solar metallicity

Abstract

In high metallicity environments the mass that black holes (BHs) can reach just after core-collapse widely depends on how much mass their progenitor stars lose via winds. On one hand new theoretical and observational insights suggest that early-stage winds should be weaker than what many canonical models prescribe. On the other hand the proximity to the Eddington limit should affect the formation of optically thick envelopes already during the earliest stages of stars with initial masses $M_{\rm ZAMS}\gtrsim 100$ M$_\odot$, hence resulting in higher mass-loss rates during the main sequence. We use the evolutionary codes MESA and Genec to calculate a suite of tracks for massive stars at solar metallicity Z$_\odot=0.014$ which incorporate these changes in our wind mass loss prescription. In our calculations we employ moderate rotation, high overshooting and magnetic angular momentum transport. We find a maximum BH mass $M_{\rm BH, max}=28.3$ M$_\odot$ at Z$_\odot$. The most massive BHs are predicted to form from stars with $M_{\rm ZAMS}\gtrsim 250$ M$_\odot$, with the BH mass directly proportional to its progenitor's $M_{\rm ZAMS}$. We also find in our models that at Z$_\odot$ almost any BH progenitor naturally evolves into a Wolf-Rayet star due to the combined effect of internal mixing and wind mass loss. These results are considerably different from most recent studies regarding the final mass of stars before their collapse into BHs. While we acknowledge the inherent uncertainties in stellar evolution modelling, our study underscores the importance of employing the most up-to-date physics in BH mass predictions.