The Influence Of Viscosities On The Structure Of Protoplanetary Disks

Accretion is a process that an astrometry virtue of its gravitational attracting andaccumulating the surrounding material. Since the accreting material tend to haveangular momentum, so this will form an accretion disk.The protoplanetary disk system includes the central star and circumambientnebula. There are two difficulties of the nebula hypothesis; one of them is how totransport the angular momentum. According to the observed solar system, the solarmass contains99.865%of the total mass of the system, and the angular momentum isless than0.6%; while the mass of other planets in the system is0.135%of the totalmass, and the angular momentum is higher than99%of the total angular. How doesthe angular momentum transport in the evolution of the protoplanetary disk? Thesecond difficulty is about that how the dusts in the protoplanetary disk accumulate toplanets and satellites and we don’t study it in this pater. We focus on that how theviscosity influences the structure of protoplanetary disks in the processes of angularmomentum transport.The evolution of the protoplanetary disk mainly depends on the redistribution ofangular momentum and mass in it. To conserve angular momentum and mass, theangular momentum of the gas transport in the protoplanetary disk transport from theinner part to the outer part of the disk, while the mass transport to the inner partspirally. At the same time, the viscosity causes shearing movement and producesheating, most of which radiates from the surface of steady disk.It is no doubt that the materials in the nebula are heated because of the viscosityand radiate to the surroundings. But the hydrodynamic viscosity alone cannot explainthe transport of the angular momentum in the protoplanetary disk. Shakura andSunyaev suggested that turbulence in the gas is the main source of the viscosity,which is thought to be a reasonable dynamical theory to explain the redistribution of angular momentum, even if the origin of the turbulence hasn’t been understood.Traditionally we adopt a viscosity parameter α to explain the enhancement of theviscosity caused by turbulence in the disk.In this article, we use the protoplanetary disk model of Jin&Sui. The modelcontains a non-uniform viscosity and quality inflows caused by molecular cloud coresgravitational collapse. Molecular cloud cores collapse from the inside out. And thecollapse forms an accretion disk system, consisting of the central star and thesurrounding nebula. Based on the hydrostatic equilibrium equation and the traditionaltheory of angular momentum. We consider the thin disk case, numerically simulatethe evolution of the protoplanetary disk, and study the influence of the viscosity onthe evolution of the protoplanetary disk.The range of the parameter α is based on the result of the numericalsimulations. For different α, we obtain the surface density, the midplane temperature,and the midplane density of different time as functions of cylindrical radius. We findthat viscosity parameter α is very important to the evolution of the protoplanetarydisk. When α is large and the protoplanetary disk doesn’t come throughgravitational instability, the surface density of the protoplanetary disk decreases, themidplane temperature decreases but the change is small compared to the surfacedensity， and the midplane density decreases. But the surface density at large radiusincreases. The surface density at small radius is inverse to α. When the disk goesthrough gravitational instability,the surface density of the protoplanetary diskdecreases sharply. The surface density of disks decreases as α increases even if thedisks are gravitationally unstable.