Nucleosynthetic Constraints on the Mass of the Heaviest Supernovae

TL;DR

This paper investigates how the maximum mass of stars that explode as supernovae affects the production of elements in the galaxy, suggesting that stars up to 18-25 solar masses could be the primary contributors.

Contribution

It introduces a model linking the upper mass limit of supernova progenitors to observed solar abundances, considering variable physics like mass loss and nuclear reaction rates.

Findings

Successful nucleosynthesis can occur with supernova cutoffs as low as 18 solar masses.

Reducing the upper mass limit increases the required supernova rate significantly.

Nucleosynthesis of certain isotopes like iron-60 and aluminum-26 is also analyzed.

Abstract

Assuming a Salpeter initial mass function and taking the solar abundances as a representative sample, we explore the sensitivity of nucleosynthesis in massive stars to the truncation of supernova explosions above a certain mass. It is assumed that stars of all masses contribute to nucleosynthesis by their pre-explosive winds, but above a certain limiting main sequence mass, the presupernova star becomes a black hole and ejects nothing more. The solar abundances from oxygen to atomic mass 90 are fit quite well assuming no cut-off at all, i.e., by assuming all stars up to 120 solar masses make successful supernovae. Little degradation in the fit occurs if the upper limit is reduced to 25 solar masses. The limit can be further reduced, but the required event rate of supernovae in the remaining range rises rapidly to compensate for the lost nucleosynthesis of the more massive stars. The nucleosynthesis of the s-process declines precipitously and the production of species made in the winds, e.g., carbon, becomes unacceptably large compared with elements made in the explosion, e.g., silicon and oxygen. However, by varying uncertain physics, especially the mass loss rate for massive stars and the rate for the neon-22 to magnesium-25 reaction rate, acceptable nucleosynthesis might still be achieved with a cutoff as low as 18 solar masses. This would require a supernova frequency three times greater than the fiducial value obtained when all stars explode in order to produce the required oxygen-16. The nucleosynthesis of iron-60 and aluminum-26 is also examined.