The first 3D MHD core-collapse progenitors II: Rotation, magnetic-field amplification, and magnetic topology

Abstract

The most energetic core-collapse supernovae are thought to arise from rapidly rotating, magnetised progenitors. However, the three-dimensional pre-collapse structure of their angular momentum and magnetic fields remains poorly constrained, limiting the realism of magnetorotational core-collapse simulations. We investigate the angular-momentum distribution, magnetic-field amplification and magnetic topology of physically consistent three-dimensional magnetohydrodynamic pre-supernova progenitors. We used Aenus-Alcar to evolve two compact Wolf--Rayet progenitors, computed with the stellar-evolution codes GENEC and MESA, through the final minutes before core collapse. Our models suggest that the rotation profile near the inner core can depart from a purely shellular distribution and reorganise toward a more cylindrical structure. In convective regions, hydrodynamic Reynolds stresses drive the flow toward an approximately constant specific-angular-momentum profile, corresponding to an average rotation profile close to $Ω\propto \varpi^{-2}$ ($\varpi$ denotes the cylindrical radius). Convective regions amplify seed magnetic fields, transported from neighbouring radiative layers, producing saturated fields with comparable toroidal and poloidal components and a topology containing substantial small-scale power. As a result, regions that are magnetically disconnected in the original one-dimensional stellar-evolution description become magnetically linked in the multidimensional models. Multidimensional evolution can substantially modify both the angular-momentum distribution and magnetic topology of pre-collapse progenitors. They provide a physically motivated basis for constructing more realistic initial conditions for magnetorotational core-collapse simulations and for improving prescriptions of magneto-convective angular-momentum transport in late stellar evolution.