# Storing magnetic fields in pre-collapse cores of massive stars

## TL;DR

This paper suggests that the radiative zone above the iron core in massive stars can store strong magnetic fields, which are amplified during collapse and may help drive supernova explosions via jet mechanisms.

## Contribution

It demonstrates that magnetic flux loops in the radiative zone can be retained and amplified during collapse, supporting the role of magnetic fields in core-collapse supernovae.

## Key findings

- Magnetic flux loops can be stored in the radiative zone due to buoyancy barriers.
- Magnetic fields can be amplified by a factor of about 100 during collapse.
- Strong magnetic fields facilitate jet-driven supernova explosions.

## Abstract

We argue that the radiative zone above the iron core in pre-collapse cores of massive stars can store strong magnetic fields. To reach this conclusion we use the stellar evolutionary code MESA to simulate the evolution of two stellar models with initial masses of 15Mo and 25Mo, and reveal the entropy profile above the iron core just before core collapse. Just above the iron core there is a thin zone with convective shells. We assume that a dynamo in these convective shells amplifies magnetic fields and forms magnetic flux loops. By considering the buoyancy of magnetic flux loops we show that the steep entropy rise in the radiative zone above the dynamo can prevent buoyancy of flux loops with magnetic fields below about 10^{13}G. When this radiative zone collapses on to the newly born neutron star the converging inflow further amplifies the magnetic fields by a factor of about a hundred. After passing through the stalled shock at about a hundred kilometres from the center, these strong magnetic fields together with instabilities can facilitate the launching of jets that explode the star in the frame of the jittering jets explosion mechanism. Our study further supports the claim for the necessity to include magnetic fields in simulating the explosion of CCSNe.