Snapshot of a magnetohydrodynamic disk wind traced by water maser observations

Abstract

The formation of astrophysical objects of different nature, from black holes to gaseous giant planets, involves a disk–jet system, where the disk drives the mass accretion onto a central compact object and the jet is a fast collimated ejection along the disk rotation axis. Magnetohydrodynamic disk winds can provide the link between mass accretion and ejection, which is essential to ensure that the excess angular momentum is removed and accretion can proceed. However, until now, we have been lacking direct observational proof of disk winds. Here we present a direct view of the velocity field of a disk wind around a forming massive star. Achieving a very high spatial resolution of about 0.05 au, our water maser observations trace the velocities of individual streamlines emerging from the disk orbiting the forming star. We find that, at low elevation above the disk midplane, the flow co-rotates with its launch point in the disk, in agreement with magneto-centrifugal acceleration. Beyond the co-rotation point, the flow rises spiralling around the disk rotation axis along a helical magnetic field. We have performed (resistive-radiative-gravito-)magnetohydrodynamic simulations of the formation of a massive star and record the development of a magneto-centrifugally launched jet presenting many properties in agreement with our observations.