Circumstellar Disk Formation in the Early Phase of Star Formation

The transport of angular momentum by magnetic fields is a crucial physical process in formation and evolution of stars and disks, and non-ideal MHD effects have significant impacts there as they redistribute magnetic flux and suppress angular momentum transport. We perform 3D radiation magnetohydrodynamic simulations including Ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields transport angular momentum so efficiently that no rotationally supported disk is formed even after the second collapse. However, with both Ohmic dissipation and ambipolar diffusion, these effects work effectively in almost the entire region within the first core and significant magnetic flux loss occurs. As a result, a rotationally supported disk is formed even before a protostellar core forms.

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