Self-similar collapse of magnetized molecular cloud cores with ambipolar diffusion and the 'magnetic flux problem' in star formation

摘要

We investigate the dynamic collapse of magnetized singular isothermal spheres in the presence of ambipolar diffusion, using a self-similarity technique. The spherical geometry, a crucial idealization first introduced by Safier, McKee, & Stahler to study the evolution of magnetized clouds, is made possible by ignoring magnetic tension forces. We find that, in the limit of a complete coupling between magnetic fields and neutral matter, magnetized spheres collapse via an expansion-wave solution, as in the (nonmagnetized)singular isothermal case. The presence of ambipolar diffusion modifies the collapse in two interesting ways.