Storing magnetic fields in pre-collapse cores of massive stars

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 M-ZAMS = 15 M-circle dot and M-ZAMS = 25 M-circle dot, 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 several x 10(12) 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 100. After passing through the stalled shock at about a 100 km from the centre, 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 core collapse supernovae.