Formation of Disks and Binaries

Abstract

Two possible outcomes are considered for the collapse of a rotating core of a molecular cloud. For the first case, two-dimensional axisymmetric hydrodynamical collapse calculations with radiative transfer are presented to study the formation of a central star and a disk. For the second case, three-dimensional calculations provide insight on the process of the formation of binary and multiple systems of protostars. In general when a protostar or fragment collapses it passes through three phases. The first, the isothermal phase, corresponds to low-density gas which is optically thin to infrared radiation. The second, adiabatic, phase starts in the central regions of the protostar or fragment when it becomes dense enough to be optically thick; thus as it compresses it heats. The third, accretion, phase starts when the central regions of the collapsing fragment reach hydrostatic equilibrium and form the core of a star. Remaining infalling material accretes onto this central object, either directly or through a disk. In the case of the axisymmetric solutions presented here, the evolution passes through all three phases. The 3-D simulations, however, are limited mainly to the isothermal phase.