Fossil Magnetic Fields and Rotational Coupling in Stars

The exchange of angular momentum (AM) between a star's core and envelope during stellar evolution is important in shaping internal rotation profiles. In massive stars, a receding convective core may leave behind stable magnetic fields that enforce partial corotation in the radiative interior, limiting differential rotation and influencing long-term AM transport.

To investigate this process, we run idealized, rotating magnetohydrodynamic (MHD) simulations using the Dedalus framework in spherical geometry. The model includes internal heating, surface cooling, and a receding convective core to study how dynamo-generated magnetic fields are generated and embedded in the radiative zone. We analyze the evolution of magnetic field geometry, temperature profiles, and differential rotation to identify the conditions under which remnant fields can enforce corotation or allow differential rotation to persist. By quantifying the strength and stability of magnetic coupling in the radiative interior, this work aims to test whether fossil magnetic fields can form persistent “magnetic webs” that regulate AM transport. The results will help interpret asteroseismic measurements of stellar rotation and link internal magnetic structure to observed stellar rotation.