Special DIX Planetary Science Seminar

We summarize essential physical processes in star formation in filamentary molecular clouds that include thermodynamics, the evolution of angular momentum, and the effect of magnetic fields. Recent advances in non-ideal magnetohydrodynamics (MHD) simulations, which cover a huge dynamic range from a molecular cloud density to stellar density, enable us to study the formation of filamentary clouds and dense cores, the realistic evolution of the magnetic field and rotation of protostars, driving of outflows and jets, and the formation of protoplanetary disks. First, we emphasize the importance of radiative heating and cooling, and describe thermal evolution in a self-gravitationally collapsing cloud and the formation of the first core and the second core. The first core gradually transforms into a circumstellar disk that eventually accretes onto the central protostar. Second, the angular momentum in a collapsing cloud is removed by MHD effects such as magnetic braking and driving of outflows and jets. The circumstellar disk is born in the "dead zone" that is the region decoupled from the magnetic field. The outer radius of the disk increases with that of the dead zone during the accretion phase. A rapid increase in the disk size occurs after depletion of the envelope. The further long-term evolution of massive disks provides realistic initial conditions and environments for planet formation in gaseous protoplanetary disks. The implication for observations of diverse property of the disk is also indicated.