Recent observations on star-forming regions have revealed that the protostellar outflows driving from the Young Stellar Objects (YSOs) show a variety of asymmetrical features. For instance, Atacama Large Millimeter/submillimeter Array observations of the protostellar environment in the Orion A Molecular cloud has reported the existence of protostars driving the asymmetrical bipolar outflows and the unipolar outflows. Structures such as the asymmetrical protostellar outflows can dramatically change the mass accretion and angular momentum transport to the protostars and protoplanetary disks. Thus, the understanding of the asymmetrical protostellar outflows is crucial for the formation and early evolution of YSOs. We perform the three-dimensional non-ideal magnetohydrodynamics simulations to investigate the formation of the asymmetrical protostellar outflows in the early evolution of YSOs formed via the collapse of magnetized and turbulent molecular cloud cores. The results show that the asymmetrical bipolar outflow is driven when the initial cloud core is sub-Alfvénic and trans-Alfvénic (the mean Alfvén Mach number of the initial cloud core is comparable to or lower than 1). However, the unipolar outflow is driven when the initial cloud core is super-Alfvénic (the mean Alfvén Mach number of the initial cloud core is higher than 1). Furthermore, we find the "protostellar rocket effect" in the unipolar outflow driving system; the linear momentum transport from the unipolar outflow causes the protostar to move from the inner to the outer regions of the cloud cores, and the resulting ram pressure suppresses the additional new outflow driving. The results indicate that the balance of the turbulent and magnetic energies of the parent cloud core plays a key role in the formation of asymmetrical protostellar outflows. The results can also explain the observed asymmetrical features of the protostellar outflows.
[Poster PDF File]