  The magnetic fields affect collapse of molecular cloud cores. Here, we
consider a collapsing core with an axial magnetic field and investigate its
effect on infall of matter and formation of accretion disk. For this purpose,
the equations of motion of ions and neutral infalling particles are numerically
solved to obtain the streamlines of trajectories. The results show that in
non-steady state of ionization and ion-neutral coupling, which is not
unexpected in the case of infall, the radius of accretion disk will be larger
as a consequence of axial magnetic field.
