  Magnetic fields play an important role in star formation by regulating the
removal of angular momentum from collapsing molecular cloud cores. Hall
diffusion is known to be important to the magnetic field behaviour at many of
the intermediate densities and field strengths encountered during the
gravitational collapse of molecular cloud cores into protostars, and yet its
role in the star formation process is not well-studied. This thesis describes a
semianalytic self-similar model of the collapse of rotating isothermal
molecular cloud cores with both Hall and ambipolar diffusion, presenting
similarity solutions that demonstrate that the Hall effect has a profound
influence on the dynamics of collapse.
  ...
  Hall diffusion also determines the strength of the magnetic diffusion and
centrifugal shocks that bound the pseudo and rotationally-supported discs, and
can introduce subshocks that further slow accretion onto the protostar. In
cores that are not initially rotating Hall diffusion can even induce rotation,
which could give rise to disc formation and resolve the magnetic braking
catastrophe. The Hall effect clearly influences the dynamics of gravitational
collapse and its role in controlling the magnetic braking and radial diffusion
of the field would be worth exploring in future numerical simulations of star
formation.
