Abstract
Recent asteroseismic observations constitute a great challenge for rotating stellar evolution models, which predict overly fast internal rotation rates when only hydrodynamic processes are included. This suggests the absence of one or several unidentified angular momentum transport processes in these models. Transport by large-scale and strong magnetic fields in the radiative zone is a promising candidate to explain the observations. While these fields might be characterised by a fossil origin, a dynamo driven by the Tayler instability in a shear flow (i.e. a Tayler-Spruit dynamo) constitutes a primary mechanism to form the necessary magnetic fields. Despite recent numerical studies, this mechanism remains poorly known. Motivated by this scenario, we investigated the Tayler-Spruit dynamo through a new set of direct 3D numerical simulations. We modelled the radiative zone as a Boussinesq stably stratified fluid whose differential rotation is maintained by a volumetric body force. Here, we report, for the first time, the coexistence of two dynamo solutions, which mainly differ by the magnetic field location (near the equator and the polar axis). While the equatorial dynamo is driven by an instability sharing both characteristics of the azimuthal magnetorotational and Tayler instabilities, we focus mainly on the newly identified polar dynamo, which is driven by the standard Tayler instability. We show that this dynamo can still operate and transport angular momentum efficiently in a strong stratification regime, with a Brunt-Väisälä frequency that is 130 times larger than the rotation rate. We extracted new scaling laws for the different magnetic field components, transport processes, and the minimum shear to trigger the Tayler instability-driven dynamo. Finally, we were able to roughly constrain the signature of the generated magnetic fields on asteroseismic modes propagating in main sequence and evolved stars. Thus, our results encourage new studies using stellar evolution models including our prescriptions and the search of asteroseismic signals impacted by large-scale azimuthal magnetic fields.