Speaker
Description
Despite significant progress in observing stellar magnetic fields, the physical processes that determine their strength and structure - likely shaped by their formation history - remain poorly understood. During the pre-main-sequence (PMS) phase, a star’s inner layers contract, gradually forming a radiative core, while its convective envelope slows due to magnetic interactions with the accretion disk and winds. This creates internal differential rotation, which can disrupt the dynamo processes generating strong dipolar fields observed in protostars. Such disruption could explain the diverse magnetic properties observed in main-sequence stars. In this talk, I’ll share our recent work on the stability of dipolar magnetic fields inherited from the protostellar phase, focusing on how large-scale radial differential rotation, driven by stellar contraction and interactions with the surrounding medium, affects them. To this aim, we developed 3D convective dynamo simulations of rotating spherical shells, where we imposed differential rotation between the inner and outer boundaries, and density and gravity profiles close to those in PMS low-mass stars, based on predictions from the 1D stellar evolution code Cesam2k20. Our results show that radial differential rotation can indeed trigger dipole collapse, leading to weaker, oscillatory magnetic fields, when it becomes stronger than the vigor of convection. We derived a collapse criterion from our 3D dynamo simulations and applied it to 1D PMS stellar evolution models, qualitatively reproducing the observed trends in the magnetic topology of low-mass stars when assuming efficient angular momentum transport in stellar radiative cores. This suggests a strong connection between stellar magnetic properties and PMS angular momentum evolution.
