THE EARLY HISTORY OF PROTOSTELLAR DISKS, OUTFLOWS, AND BINARY STARS

In star formation, magnetic fields act as a cosmic angular momentum extractor that increases mass accretion rates onto protostars and, in the process, creates spectacular outflows. However, recently it has been argued that this magnetic brake is so strong that early protostellar disks—the cradles of planet formation—cannot form. Our three-dimensional numerical simulations of the early stages of collapse (≲105 yr) of overdense star-forming clouds form early outflows and have magnetically regulated and rotationally dominated disks (inside 10 AU) with high accretion rates, despite the slip of the field through the mostly neutral gas. We find that in three dimensions magnetic fields suppress gravitationally driven instabilities that would otherwise prevent young, well-ordered disks from forming. Our simulations have surprising consequences for the early formation of disks, their density and temperature structure, the mechanism and structure of early outflows, the flash heating of dust grains through ambipolar diffusion, and the origin of planets and binary stars.