The effect of external pressure & magnetic field in star formation: The critical mass model

Theoretical work addressing the role of external pressure with magnetic fields in collapsing molecular clouds is important in building a comprehensive theory of star formation(SF). In many SF studies turbulence, magnetic fields, and self-gravity are described as the key dynamical processes involved in SF. However, the importance of external pressure in collapsing strongly magnetized clouds has not yet been particularly explained. Magnetic fields transport excess angular momentum from the central core while external pressure compresses the cloud. Thus the outflow of angular momentum, and on the other hand, the compression made by external pressure are the cause for matter falling onto the central core from the envelope. Therefore, external pressure facilitates the collapse of gas and the inflow of matter. In this work, we show theoretically how the strong magnetic field is dragged inward by the external pressure during the core collapse and formulate the critical mass of the core in the presence of external pressure.