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K. Tassis (University of Chicago), T. Ch. Mouschovias (University of illinois)
We follow the formation and evolution of a molecular cloud core from mean molecular cloud densities to a density enhancement of twelve orders of magnitude. It is in this high density regime that a hydrostatic protostellar object forms, and the magnetic flux problem of star formation is resolved. We simulate the evolution of the core using an adaptive-grid numerical code, which follows the nonideal six-fluid MHD equations, and accounts explicitly and self-consistently for gravity, thermal pressure, the magnetic field, cosmic-ray and radioactivity-induced ionization, and the chemical and dynamical effects of dust grains. We evaluate the relative importance of different magnetic flux-loss mechanisms (ambipolar diffusion and Ohmic dissipation) in the resolution of the magnetic flux problem of star formation, and we identify the density regime where Ohmic dissipation dominates magnetic losses. In the high-density central parts of the core, the magnetic field acquires and almost spatially uniform configuration, with a value which, at the end of our calculation is found to be in excellent agreement with meteoritic measurements of magnetic fields in the protosolar nebula. After a hydrostatic protostellar object is formed, we continue to follow the evolution of the isothermal disk surrounding it and supplying it with accreted matter. We do so by introducing a "central sink", which allows us to exclude the central region from our computations, while still accounting for the physical effects of the accumulating mass and magnetic flux. In this way, we follow the accretion process onto the protostar until one solar mass is accumulated in the central sink. During this phase, we discover exciting new phenomena, such as the formation and dissipation of a series of magnetically driven radial shocks that occur in a quasi-periodic fashion.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.