The Hall effect in accretion flows

Magnetic diffusion in accretion flows changes the structure and angular momentum of the accreting material. We present two power-law similarity solutions for flattened accretion flows in the presence of magnetic diffusion: a secularly evolving Keplerian disc and a magnetically diluted free fall on to the central object. The influence of Hall diffusion on the solutions is evident even when this is small compared to ambipolar and Ohmic diffusion, as the surface density, accretion rate and angular momentum in the flow all depend upon the product ηH(B · Ω), and the inclusion of Hall diffusion may be the solution to the magnetic braking catastrophe of star formation simulations.