A crucial piece of the puzzle for understanding how disks of gas and dust accrete to form stars and planets is presented in a paper published online in Nature Astronomy this week. The study reports the observation of rotation in a jet of material launched from the innermost region of a disk around a forming star.
The disks of gas and dust around young stars have much more angular momentum than the stars at their centres. In order for the disk material to fall into and feed the forming star, that angular momentum must be removed, or the star would tear itself apart (dubbed the angular momentum problem). The bulk of the angular momentum leaves the system as a large-scale, wide-angle, low-velocity outflow called a disk wind, allowing material to move inwards.
Chin-Fei Lee and colleagues observed that a narrow, high-velocity jet that is launched very close to the star removes any residual angular momentum, allowing disk material to accrete onto the star itself. They used the Atacama Large Millimeter/submillimeter Array to peer into the region closest to HH 212, a star known for its extensive bipolar jet. They identify several clumps of material within the beam of the jet that are spinning. Although similar observations have been carried out before, none have been able to probe the rotation in the knots of material closest to the star. The authors find that the jet removes mass from the system, carrying off excess angular momentum with it.