Flows during star formation: A self-similar perspective

Stars form in molecular clouds by the gravitational collapse of dense gas. So one would expect that infall motions would dominate the gas dynamics around forming stars. However, it is precisely the opposite phenomenon that is primarily observed. Outflow motions prevail around both low and high mass young stellar objects. Hence, how is a star simultaneously a source of both powerful ejections and infall? We present here the theoretical basis and the main characteristics of a family of self-similar models that could possibly help to understand this paradox. The models take into account the heating of the central protostar for the deflection and acceleration of the gas. The models make room for all the ingredients observed around the central objects, i.e. molecular outflows, jets, accretion disks and infalling envelopes. We suggest that radiative heating and magnetic field may ultimately be the main energy sources driving outflows. We also show potential consequences of the models on the history of star formation.