Star formation and the singular isothermal sphere

We caution against approximating the initial conditions for protostellar collapse with a singular isothermal sphere. First, it is very unlikely that nature can assemble anything like a singular isothermal sphere. Secondly, collapse of a singular isothermal sphere would seem to be severely prejudiced against binary formation — either by fragmentation during collapse, or by disc instability following collapse. It is therefore appropriate to explore star formation paradigms which (a) involve initial conditions which are far less focused than the singular isothermal sphere, and (b) take into account impulsive dynamical and thermodynamic processes — reflecting the rapidly varying environments in which stars are formed. Even in relatively quiescent regions like Taurus, such processes must be reckoned with; they cannot realistically be relegated to the status of small perturbations on an essentially quasistatic theme.