A magnetized protostellar jet launched from the innermost disk at the truncation radius.

Protostellar jets form when part of the accreting material is energetically ejected from the vicinity of protostars. Understanding where and how they are launched and collimated is crucial to determining their role in the accretion process. The HH 211 jet is a highly collimated, magnetized jet associated with a rotating disk around a young protostar. With Atacama Large Millimeter/submillimeter Array, we have resolved a pristine molecular spine at its base down to the disk. This spine has a high velocity of ~ 107 ± 8 km s but a slow rotation with a specific angular momentum of ~ 4 ± 1 au km s, suggesting it to be launched at ~ 0.021 ± 0.005 au in the disk, providing the most stringent constraint yet on current magneto-centrifugal theories of jet production. Quantitative modeling supports the interpretation that the molecular spine represents the dense central component of a magnetized radial wind. This wind, launched by magneto-centrifugal force at the innermost edge of the disk-the truncation radius, removes residual angular momentum from the disk, enabling disk material to accrete onto the protostar. The toroidal field strength to collimate the dense spine in the model also agrees with that previously measured in the jet.