Numerical calculations of the collapse of nonrotating, magnetic gas clouds
Abstract
Results of the first selfconsistent numerical calculations of the dynamic collapse of a magnetized protostellar gas cloud are presented. Symmetry about an axis parallel to the initial magnetic field direction has been assumed, so that the calculations could be performed on a twodimensional grid. Also, the cloud was taken to be nonrotating and isothermal, and the magnetic field was assumed to remain frozen in to the gas. As starting models for the calculations, gas spheres with uniform density and magnetic field were used. The time evolution of the clouds has been calculated for roughly two initial freefall times, at which point the central density has increased by a factor of approximately 10,000 to 1,000,000. Several such calculations have been performed for different values of the cloud's initial thermal, magnetic, and gravitational energies. In virtually all cases it is found that, once a flattened core forms in the cloud, the central magnetic field strength, B, varies with gas density, rho, according to (d log B/d log rho) = 1/2. This behavior is independent of the initial energy ratios mentioned above. It is also found that the magnetic field is able to prevent completely the collapse of part of the outer envelope of the cloud.
 Publication:

The Astrophysical Journal
 Pub Date:
 July 1980
 DOI:
 10.1086/158098
 Bibcode:
 1980ApJ...239..166S
 Keywords:

 Gravitational Collapse;
 Interstellar Gas;
 Interstellar Magnetic Fields;
 Magnetic Clouds;
 Magnetohydrodynamics;
 Plasma Clouds;
 Protostars;
 Stellar Evolution;
 Field Strength;
 Gas Density;
 Mathematical Models;
 Numerical Analysis;
 Astrophysics