Formation of protostars in collapsing, rotating, turbulent clouds
Abstract
Collapse and star formation processes in rotating turbulent interstellar gas clouds have been studied. For this purpose numerical collapse calculations have been performed for a number of representative cases. These calculations have been carried out by a twodimensional hydrodynamical computer code, which solves the equations of hydrodynamics explicitly, coupled to the Poisson equation. The computer code has been written especially for this work and has been thoroughly tested. The calculations in this work have been performed with an effort to obtain physically reliable results (by repeating the same calculations with different numerical spatial resolutions). A physical mechanism for angular momentum transport by turbulent viscosity has been proposed and incorporated in new collapse calculations. The main results can be summarized as follows:
1. When there is no physical mechanism for angular momentum transport, the result of the collapse is a ringlike structure. If the rotation is fast enough, a quasistatic mild ringlike structure inside a flattened configuration forms. In the case of slower rotation a deep collapse with a ring ensues. The ring collapses onto itself, and its density grows up to the point where it becomes opaque. This result supports the findings of Bodenheimer and Tscharnuter.
2. The turbulent viscosity affects the nature of the collapse. The results of collapse calculations with turbulent viscosity are radically different from the respective "nonviscous" calculations. The angular momentum transport interferes with the ring formation and enables the formation of a central dense and opaque region. This region is surrounded by a flat disk.
3. For the two cases studied, the mass of the central object is a major fraction (30%) of the total mass of the system.
4. The exact form of the central object and its ultimate fate depend on the parameters, especially β (β ≡ rotational energy/gravitational energy) and Re (turbulent Reynolds number).
5. The present calculations cannot predict the future evolution of the central object because they have an insufficient spatial resolution at the center and the isothermal approximation breaks down. However, it seems likely that the collapse with turbulent viscosity leads to the formation of a central protostar surrounded by a disk (protoplanetary nebula) when the rotation is slow enough and the turbulence efficient. When the rotation is fast or the turbulent transport less efficient, the central opaque object is very flat. This raises the possibility of multiple system formation (e.g., binary).
6. The importance of this work lies in the fact that a new theoretical model is proposed, in which a central protostar forms as a result of the collapse of a protostellar rotating cloud.
 Publication:

The Astrophysical Journal
 Pub Date:
 May 1981
 DOI:
 10.1086/158871
 Bibcode:
 1981ApJ...245..934R
 Keywords:

 Gravitational Collapse;
 Interstellar Gas;
 Protostars;
 Stellar Evolution;
 Stellar Rotation;
 Turbulent Diffusion;
 Angular Momentum;
 Boundary Value Problems;
 Equations Of Motion;
 Hydrodynamic Equations;
 Nebulae;
 Rotating Fluids;
 Stellar Models;
 Transport Properties;
 Astrophysics