Long-term Protoplanetary Disk Evolution from Molecular Cloud Core Collapse and Implications for Planet Formation. I. Weak and Moderate Disk Self-gravities

We construct a one-dimensional protoplanetary disk model to investigate long-term disk evolution from molecular cloud core collapse. To obtain details of disk evolution, instead of solving the traditional diffusion equation for disk surface density, we suggest a set of equations derived from the basic principles of fluid mechanics. Effects of infalling material, magnetorotational instability, and disk self-gravity are taken into account. According to the role of disk self-gravity, we find that disks can be classified into three types. For a type I disk, disk self-gravity is not important. For a type II disk, disk self-gravity has effects on both disk scale height and gas radial motion. In addition, gravitational instability can cause the transport of angular momentum. For a type III disk, disk self-gravity plays a dominant role in disk evolution. In this paper, we focus on the first two types and the investigation of the third one is presented in a companion paper. For each disk, we find that there are three phases during evolution. Phase 1 is the very early phase during which the radial velocity is on the order of 10(6) cm s(-1) and the transport of angular momentum caused by viscosity is not important. Phase 2 begins when a rotationally supported disk is formed. From this phase, viscosity plays a role in the transport of angular momentum. When the infall ends, phase 3 begins. Since angular velocity is calculated directly, we can reveal the non-Keplerian effect, which has important effects on the radial drift of solids and planetesimal formation.