Mixing in Zero and Solar Metallicity Supernovae

TL;DR

This study uses 2D simulations to explore how metallicity and star type influence mixing and fallback in supernovae, revealing differences in nucleosynthesis and suggesting the importance of explosion asymmetries.

Contribution

It provides new insights into how metallicity and stellar structure affect supernova mixing, fallback, and nucleosynthesis, highlighting the need to consider asymmetries.

Findings

Zero metallicity stars show less mixing and more fallback than solar metallicity stars.

Ejected iron and intermediate elements are insufficient to match observed abundance patterns.

Heavy element velocities are lower than observed in SN 1987A, indicating asymmetric explosion effects.

Abstract

Two-dimensional simulations of mixing and fall back in non-rotating massive stars have been carried out using realistic initial models for the presupernova star and assuming standard spherically symmetric explosions of 1.2*10^51ergs. Stars of 15 and 25 solar masses with both primordial and solar composition were modeled. The zero metallicity supernova progenitors were compact blue stars and the amount of Rayleigh-Taylor induced mixing in them was greatly reduced compared with what was seen in the red supergiants with solar metallicity. The compact zero-metal stars also experienced more fallback than their solar metallicity counterparts. As a result, the ejected nucleosynthesis from the two populations was very different. For the simple explosion model assumed, low metallicity stars ejected ejected too little iron and intermediate mass elements even to explain the abundance patterns in the most iron-poor stars found to date, suggesting that some important ingredient is missing. Rotation is likely to alter these conclusions by producing a greater fraction of red supergiants among Population III stars. The velocities of the heavy elements in all models considered - both red and blue supergiants - were less than observed in SN 1987A, suggesting that at least occasionally, asymmetric aspects of the explosion mechanism and fallback play a major role in mixing.