The last five minutes of evolution of magnetic fields and rotation in massive stars

• Autores: Adam Griffiths
• Directores de la Tesis: Miguel-Ángel Aloy Toras (dir. tes.) , Martin Franz Obergaulinger (dir. tes.)
• Lectura: En la Universitat de València ( España ) en 2026
• Idioma: inglés
• Número de páginas: 351
• Tribunal Calificador de la Tesis: Raphael Hirschi (presid.) , Michael Gabler (secret.) , Sylvia Esktröm (voc.)
• Programa de doctorado: Doctor en Programa Oficial de Posgrado en Física
• Menciones:
  • Internacional
• Calificación: Sobresaliente Cum Laude
• Enlaces
  • Tesis en acceso abierto en:  TESEO  RODERIC 
• Resumen

  • Massive stars are the progenitors of core-collapse supernovae. Those that rotate and host magnetic fields, as many do, may produce even more powerful magneto-rotational explosions, responsible for some of the most energetic events in the Universe and for the synthesis of many heavy elements. The collapsing core ultimately forms either a neutron star or a black hole. Neutron stars may become magnetars, which possess the strongest magnetic fields known, while black holes can be studied through gravitational-wave observations of mergers, enabling constraints on their mass distribution. Understanding the fate of massive stars is therefore a key problem in astrophysics and, in the case of rotating and magnetised stars, remains only partially explored.Core-collapse simulations rely on multi-dimensional magnetohydrodynamic (MHD) calculations, which require suitable progenitor models. These progenitors are typically produced using stellar-evolution codes that evolve massive stars from birth to collapse. Because such codes must cover vast ranges of length and time scales, they are generally limited to one-dimensional calculations and use prescriptions to approximate inherently multi-dimensional processes such as convection, rotation, and magnetisation.As a result, commonly used core-collapse progenitors provide only approximate estimates of magnetic-field strength, geometry, and location, often based on local instability arguments. To improve this situation, we have, for the first time, simulated fully multi-dimensional MHD progenitors during the final minutes preceding core collapse.We incorporated the effects of the magneto-rotational instability into the stellar-evolution code GENEC and implemented additional physics required to reach collapse conditions. One-dimensional progenitors produced with GENEC, together with models computed using MESA from Aguilera-Dena (2020), were mapped into the MHD code Aenus-ALCAR. We developed a hydrostatic-equilibrium-preserving mapping algorithm based on Zingle (2002). Because convective regions are turbulent but initially velocity-free, we introduced perturbation velocity fields to reduce transient adjustment phases and reconstructed a multi-dimensional rotation profile consistent with the stellar-evolution models. We generated two rotating, magnetised progenitors evolved for several minutes prior to collapse.These simulations allow us to address key questions regarding internal magnetic fields, silicon-shell burning, core contraction, and the interplay between convection, rotation, and magnetisation. We find strong magnetic fields in both convective and radiative regions, with significant amplification in convective zones due to turbulent motions. Notably, magnetic fields can survive within convective shells, exhibiting topologies that differ substantially from those predicted in radiative regions and from standard stellar-evolution assumptions.Our models therefore display magnetic fields with large coherence lengths, creating direct connections within and between neighbouring shells. Such geometries are crucial for explosion dynamics and strongly influence the properties of the resulting compact object. We also find that magnetic-field structure is sensitive to the behaviour of convection and rotation during the final minutes before collapse. These results provide guidance for improving stellar-evolution models, particularly in their treatment of mixing-length theory and rotation during advanced burning stages.Finally, our models serve as initial conditions for a new generation of magneto-rotational explosion simulations and support progress in understanding compact objects, gamma-ray bursts, and supernovae. We aim to use these results to develop improved prescriptions for rotation and magnetic fields in stellar-evolution codes, enabling more realistic initial conditions for multi-dimensional core-collapse simulations without requiring full three-dimensional evolution to collapse.