Modeling the origin of the rotation of massive stars

Context. We explore the origins behind the rotation rates of massive stars, accounting for the fact that in contrast to their low-mass siblings, most massive stars do not have detectable magnetic fields. Thus, the star-disk interaction models typically used to simulate the formation of rotating low-mass stars do not apply. Aims. We investigate whether the magnetic fields of protostellar jets present in the parent molecular cloud prevent the protostar from reaching the critical angular velocity. Methods. Starting from the gravitational collapse of a molecular cloud, we ran two 2D radiation-gravito-magnetohydroynamical simulations to study the formation of an accretion disk and the launching of magnetically driven protostellar outflows. In particular, we were interested in following the formation of a magnetocentrifugal jet originating from the protostar and inner disk. We then studied the angular momentum transfer from the disk and jet onto the protostar. Finally, we computed the 1D stellar evolution models of the pre-main sequence, including our results from the disk-jet simulations and following the angular momentum redistribution within the structure of the protostar. Results. We found that the angular momentum transported outwards by magnetically driven protostellar outflows is sufficient for keeping the protostar below the critical speed at all times. Moreover, we were able to link the strength of the jet and, as a result, the rotation rate at the end of the accretion epoch as well, to the initial conditions for star formation. Our results show that the jet strength produces a variety of stellar rotation rates, suggesting that protostellar jets play a dominant role in fixing the rotation rate of massive stars.