2004MNRAS.347..873M

We argue that the outbursts of the FU Orionis stars occur on time-scales which are much longer than expected from the standard disc instability model with α_c≳ 10^–3. The outburst, recurrence and rise times are consistent with the idea that the accretion disc in these objects is truncated at a radius R_i∼ 40 R_☉. In agreement with a number of previous authors, we suggest that the inner regions of the accretion discs in FU Ori objects are evacuated by the action of a magnetic propeller anchored to the central star. We develop an analytic solution for the steady-state structure of an accretion disc in the presence of a central magnetic torque, and present numerical calculations to follow its time evolution. These calculations confirm that a recurrence time that is consistent with observations can be obtained by selecting appropriate values for viscosity and magnetic field strength.