Star formation in rotating, magnetized molecular disks

Abstract

The discovery of dense, rotating molecular disks associated with protostars and bipolar outflows suggests that massive (M/sub d/approx.10/sup 1.5/ M/sub sun/) objects have not shed their excessive (happrox.10/sup 22/ cm/sup 2/ s/sup -1/) angular momentum by the time protostellar activity begins. This paper presents a theory for star formation in rotating disks in which accretion onto the protostellar core produces FUV radiation which heats the disk surfaces out to large radii. A hydromagnetic wind results in which heated gas is driven out along field lines which thread the disk and are aligned with the disk rotation axis. For accretion luminosities of 4 x 10/sup 37/ ergs s/sup -1/, a highly ionized flow inside 10/sup 15/ cm with M/sub ion/ up to 10/sup -6/ M/sub sun/ yr/sup -1/ is expected, and a much more massive, neutral component carrying M/sub w/ = 10/sup 22/ g s/sup -1/ from disk radii r>10/sup 15/ cm. Terminal wind speeds of 50 km s/sup -1/ are achieved in this bipolar outflow. The centrifugally driven wind removes angular momentum from the disk at rates high enough to brake it down to protostellar specific values in 10/sup 5/ yr. The wind drives an accretion rate through the diskmore » at rates which are consistent with the accretion luminosity. This global analysis of star formation in a rotating, magnetized disk offers a unifying scheme for understanding both star formation and bipolar outflows. The disks are ''flywheels'' that store rotational energy which is released at a rate dictated self-consistently by the rate at which accretion onto the central protostellar core occurs. The disks in which massive stars form are predicted to be dense (10/sup 8/ cm/sup -3/) and have rotation speeds of 4 km s /sup -1/, scales of order 5 x 10/sup 16/ cm, masses of order 10/sup 2/ M/sub sun/, and axial ratios of 0.2.« less