The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability

TL;DR

This study explores how magneto-rotational instability in core-collapse supernovae can lead to diverse nucleosynthesis outcomes, including weak, intermediate, and regular r-process element production, aligning with observed stellar abundance patterns.

Contribution

It introduces detailed MHD simulations of magneto-rotational supernovae that resolve the instability and demonstrate varied r-process nucleosynthesis outcomes based on magnetic field strength.

Findings

Weak r-process produces nuclei up to A~130.

Stronger magnetic fields yield solar-like r-process patterns.

Intermediate r-process matches abundance patterns in metal-poor stars.

Abstract

We investigated r-process nucleosynthesis in magneto-rotational supernovae, based on a new explosion mechanism induced by the magneto-rotational instability. A series of axisymmetric magneto-hydrodynamical simulations with detailed microphysics including neutrino heating is performed, numerically resolving the magneto-rotational instability. Neutrino-heating dominated explosions, enhanced by magnetic fields, showed mildly neutron-rich ejecta producing nuclei up to $A \sim 130$ (i.e. the weak r-process), while explosion models with stronger magnetic fields reproduce a solar-like r-process pattern. More commonly seen abundance patterns in our models are in between the weak and regular r-process, producing lighter and intermediate mass nuclei. These {\it intermediate r-processes} exhibit a variety of abundance distributions, compatible with several abundance patterns in r-process-enhanced metal-poor stars. The amount of Eu ejecta $\sim 10^{-5} M_\odot$ in magnetically-driven jets agrees with predicted values in the chemical evolution of early galaxies. In contrast, neutrino-heating dominated explosions have a significant amount of Fe ($^{56}{\rm Ni}$) and Zn, comparable to regular supernovae and hypernovae, respectively. These results indicate magneto-rotational supernovae can produce a wide range of heavy nuclei from iron-group to r-process elements, depending on the explosion dynamics.