Collapse and Fragmentation of Magnetic Molecular Cloud Cores

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The initial stages of star formation through collapse and fragmentation of magnetized molecular cloud cores are analyzed by computational models which include the effects of magnetic fields and radiative transfer. Observations show that magnetic fields are important for the dynamics of molecular cloud complexes. The goal is to integrate more detailed physics of magnetic fields into the simulations to better understand the fragmentation of dense molecular cloud cores and the origin of binary and multiple star systems.The important effects of magnetic field interactions can be treated approximately by including extra terms in the equation of state or by modifying gravity terms. Previously the investigator had implemented the magnetic field effects in his code by treating it as a scalar pressure term, by the dilution of gravity (representing magnetic field line tension), by a magnetic braking approximation, and by parameterizations of the loss of pressure support through ambipolar diffusion of magnetic fields. Here these previous approximations in the principal investigator's code are replaced with a simplified magnetohydrodynamics (MHD) routine that includes a numerical solution of the magnetic induction equation, and proper treatment of ambipolar diffusion. The results from the updated code are compared to the previous pseudo-magnetic calculations, and to results from the University of Chicago's FLASH adaptive mesh refinement code. The comparisons should provide good insights about the robustness or weaknesses of the different computational approaches to model the physics of magnetic field interactions during cloud core fragmentation and collapse.