arXiv subjects

Adam Griffiths

Publications and source records attributed to Adam Griffiths.

3 recordsLinked to original sources

arXiv2026

The first 3D MHD core-collapse progenitors I: General properties, convection and nuclear burning

The most energetic core-collapse supernovae are thought to arise from rapidly rotating, magnetised progenitors, yet the three-dimensional structure of their pre-collapse interior remains poorly constrained, and realistic distributions of magnetic fields, angular momentum, and convective asphericities are still lacking. We construct physically consistent three-dimensional pre-supernova progenitors including rotation and magnetic fields. In this first paper, we focus on the behaviour of turbulence and nuclear burning in the shells surrounding the stellar core, and assess their deviations from one-dimensional stellar-evolution models. We used Aenus-ALCAR to perform three-dimensional magnetohydrodynamic (MHD) simulations of two compact Wolf--Rayet progenitors obtained from the stellar evolution codes GENEC and MESA. The models were mapped into the multidimensional domain several minutes before collapse and evolved until the onset of core collapse. We find that in extended oxygen-burning shells, turbulent velocities exceed the standard mixing-length-theory (MLT) predictions by approximately a factor of two. In contrast, a thin silicon-burning shell is poorly described by MLT: mixing is reduced near both shell boundaries, and the inferred effective diffusion profile departs significantly from the standard one-dimensional prescription. These differences directly affect the spatial extent and efficiency of nuclear burning. We present the first 3D MHD pre-supernova progenitors of this kind, suitable for subsequent collapse and explosion calculations, and show that multidimensional effects can significantly modify turbulent mixing and shell burning during the final stages of massive-star evolution. We propose prescriptions to account for these effects in the advanced phases of stellar evolution.

astro-ph.SR↗

arXiv2026

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

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 $\Omega\propto \varpi^{-2}$ ($\varpi$ 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.

astro-ph.SR↗

arXiv2024

Evolving massive stars to core collapse with GENEC: Extension of equation of state, opacities and effective nuclear network

Stars with initial mass above roughly 8 solar masses will evolve to form a core made of iron group elements at which point no further exothermic nuclear reactions between charged nuclei may prevent the core collapse. Electron captures, neutrino losses, and the photo-disintegration of heavy nuclei trigger the collapse of these stars. Models at the brink of core collapse are produced using stellar evolution codes and these pre-collapse models may be used in the study of the subsequent dynamical evolution (including their explosion as supernovae and the formation of compact remnants such as neutron stars or black holes). We upgrade the physical ingredients employed by the GENeva stellar Evolution Code, GENEC, so that it may cover the regime of high temperatures and high densities required to produce progenitors of core-collapse. We have improved GENEC in three directions, equation of state, the nuclear reaction network and the radiative and conductive opacities adapted for the computation of the advanced phases of evolution. We produce a small grid of pre-supernova models of stars with zero-age main sequence masses of 15, 20 and 25 solar masses at solar and less than half solar metallicities. The results are compared with analogous models produced with the MESA code. The global properties of our new models, particularly of their inner cores, are comparable to models computed with MESA and pre-existing progenitors in the literature. Between codes the exact shell structure varies impacting explosion predictions. Using GENEC with state-of-the-art physics, we have produced massive stellar progenitors prior to collapse. These progenitors are suitable for follow-up studies, including the dynamical collapse and supernova phases. Larger grids of supernova progenitors are now feasible, with potential for further dynamical evolution.

astro-ph.SR↗