Different Modes of Star Formation: Gravitational Collapse of
  Magnetically Subcritical Cloud
  Star formation in magnetically subcritical clouds is investigated using a
three-dimensional non-ideal magneto-hydrodynamics simulation. Since rapid cloud
collapse is suppressed until the magnetic flux is sufficiently removed from the
initially magnetically subcritical cloud by ambipolar diffusion, it takes >
5-10t_ff to form a protostar, where t_ff is the freefall timescale of the
initial cloud. The angular momentum of the star forming cloud is efficiently
transferred to the interstellar medium before the rapid collapse begins, and
the collapsing cloud has a very low angular momentum. Unlike the magnetically
supercritical case, no large-scale low-velocity outflow appears in such a
collapsing cloud due to the short lifetime of the first core. Following
protostar formation, a very weak high-velocity jet, which has a small momentum
and might disappear at a later time, is driven near the protostar, while the
circumstellar disc does not grow during the early mass accretion phase. The
results show that the star formation process in magnetically subcritical clouds
is qualitatively different from that in magnetically supercritical clouds.
