‘Cored apple’ bipolarity: a global instability to convection in radial accretion?

We propose that the prevalence of bipolarity in young stellar objects is due to the fine tuning that is required for spherical accretion of an ambient medium on to a central node. It is shown that there are two steady modes that are more likely than radial accretion, each of which is associated with a hyperbolic central point in the meridional stream lines, and consequently with either an equatorial inflow and an axial ejection or an axial inflow and an equatorial ejection. In each case the stream lines pass through a thick accretion torus, which is better thought of as a standing pressure wave rather than as a relatively inert Keplerian structure