Supernovas are known for producing heavy elements through a process called nucleosynthesis. Nucleosynthesis occurs during the final stages of a massive star's collapse. As the star's core collapses, it creates an environment where temperature, density, and pressure are extremely high – ideal conditions for protons and neutrons to come together to form new atomic nuclei.

A new study used simulations to investigate the causes for variations in the production of manganese and nickel. The research, published in the journal Nature Astronomy on Jan. 30, uncovers that mixing between ejecta from the collapsing core and the surrounding star controls how much nickel-56 and manganese-56 forms.

"Manganese-56 and nickel-56 are produced by the neutron capture process, r-process, during which atomic nuclei absorb neutrons until they reach an unstable configuration that cannot capture any more," said University of Alabama astrophysicist Matthew Mumpower, lead author of the study. "The absorption of neutrons rapidly leads to the formation of very heavy nuclei, but under specific conditions, the nuclei can take paths to bypass the formation of highly unstable nuclei, allowing them to form stable iron-group nuclei like nickel-56 and manganese-56."

The nucleosynthesis of manganese-56 and nickel-56 is interesting because these elements are not found in supernova ejecta in equal quantities. Observations show that supernovas produce up to 10 times as much nickel-56 as manganese-56. Understanding the origin of this manganese-56 and nickel-56 ratio could help scientists understand the explosion mechanism of supernovas.

The team's simulations followed how supernovas explode while also solving the nuclear physics involved with the production of elements during nucleosynthesis. They found that the key to understanding the manganese-56 to nickel-56 ratio lies in the mixing of two different layers in the presupernova star.

"The core's environment allows for efficient production of nickel-56 and manganese-56 if these layers mix," said Mumpower.

While it is expected that mixing occurs, the details of the mixing during the explosion and its impact on the relative production of manganese-56 and nickel-56 are still uncertain.

"What we showed in our simulations is that how much mixing occurs, how far out the mixing occurs, and the time during the explosion that the mixing happens are important to explaining why the production of nickel-56 is often significantly larger than the production of manganese-56," said Mumpower. "It is clear that simulations that do not treat the mixing and nucleosynthesis in a consistent manner will provide incomplete or incorrect results."