Very massive star winds as sources of the short-lived radioactive isotope $^{26}$Al

TL;DR

This study investigates the role of very massive stars (150-300 solar masses) in producing the radioactive isotope $^{26}$Al through stellar winds, highlighting their potentially significant contribution to galactic nucleosynthesis.

Contribution

It is the first to analyze the $^{26}$Al contribution from very massive stars via stellar winds, considering rotation, metallicity, and galactic distribution.

Findings

Very massive stars can significantly increase $^{26}$Al in the galaxy.

Stellar winds from very massive stars contribute up to 150% more $^{26}$Al.

Metallicity influences the $^{26}$Al production efficiency.

Abstract

The $^{26}$Al short-lived radioactive nuclide is the source of the observed galactic diffuse $\gamma$-ray emission at 1.8 MeV. While different sources of $^{26}$Al have been explored, such as AGB stars, massive stars winds, and supernovae, the contribution of very massive stars has never been studied. We study the stellar wind contribution of very massive stars, i.e stars with initial masses between 150 and 300 M$_\odot$, to the enrichment in $^{26}$Al of the galactic interstellar medium. We discuss the production of $^{26}$Al by studying rotating and non-rotating very massive stellar models with initial masses between 150 and 300 M$_\odot$ for metallicities Z=0.006, 0.014, and 0.020. We confront this result to a simple Milky Way model taking into account both the metallicity and the star formation rate gradients. We obtain that very massive stars in the Z=0.006-0.020 metallicity range might be very significant contributors to the $^{26}$Al enrichment of the interstellar medium. Typically, the contribution of the winds of massive stars to the total quantity of $^{26}$Al in the Galaxy increases by 150\% when very massive stars are considered. Very massive stars, despite their rarity, might be important contributors to $^{26}$Al and overall very important actors for nucleosynthesis in the Galaxy.