THE FORMATION PHASE OF THE SOLAR NEBULA

Hydrodynamical calculations of the collapse of an axisymmetric, rotating protostellar cloud, with radiation transport and without magnetic fields, are presented. The collapse is assumed to start from a centrally condensed sphere of radius 5 × 1015 cm, a mean density of 4 × 10-15 g cm-3, a total mass of 1 M⊙ and a total angular momentum of 1053 g cm2 s-1. The numerical grid is chosen to resolve the region of disk formation between 1 and 60 AU from the center. The calculations are continued until a relatively thick, warm disk, close to hydrostatic equilibrium, is formed. Frequency-dependent radiative transfer calculations show how the emergent spectrum of the structure depends upon viewing angle with respect to the rotation axis and how the observed isophotal contours should depend on wavelength and viewing angle. The central part of the protostar, interior to 1 AU, is not resolved numerically but is modeled approximately. At the end of the calculation this region is found to have a mass of 0.6 M⊙ and a ratio of rotational to gravitational energy of ∼0.4, sufficiently large to be unstable to nonaxisymmetric perturbations. Although the disk is gravitationally stable according to the local Toomre criterion, the nonaxisymmetric structure in the center is likely to lead to angular momentum transport.