FURTHER-STUDIES OF GRAVITATIONALLY UNSTABLE PROTOSTELLAR DISKS

Models of the solar nebula reveal that it might have been gravitationa lly unstable, both early and later in its evolution. Such instabilitie s produce density waves and associated gravitational torques, which ar e potent agents of angular momentum transport. In previous work, we co nducted a series of numerical simulations designed to quantify the eff ects of gravitational instabilities in a generalizable way (Tomley, Ca ssen, & Steiman-Cameron 1991). Here we present a second series of simu lations in which we examine disks of greater size, increased star/disk mass ratio, and flatter surface density distribution than those in ou r initial study. The purpose is to represent disks at a later stage of evolution than those already studied, to test the quantitative relati ons derived in our earlier work and to explore the effects of mass rat io on the results. The new results indicate that the tendencies for un stable, uncooled disks to heat to stability and for dynamical evolutio n rates to be proportional to cooling rates are general characteristic s of the behavior of gravitationally unstable disks. Nevertheless, the re are quantitative, and (for strong cooling) even qualitative differe nces that are revealed in the new simulations, particularly with regar d to the cooling rates at which clumping tends to occur.