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Magnetic Propeller Outflows

R. V. E. Lovelace, M. M. Romanova, G. S. Bisnovatyi‐Kogan
1999 Astrophysical Journal  
A model is developed for magnetic 'propeller'-driven outflows which cause a rapidly rotating magnetized star accreting from a disk to spin-down. Energy and angular momentum lost by the star goes into expelling most of the accreting disk matter. The theory gives an expression for the effective Alfven radius $R_A$ (where the inflowing matter is effectively stopped) which depends on the mass accretion rate, the star's mass and magnetic moment, and the star's rotation rate. The model points to a
more » ... odel points to a mechanism for 'jumps' between spin-down and spin-up evolution and for the reverse transition, which are changes between two possible equilibrium configurations of the system. In for example the transistion from spin-down to spin-up states the Alfven radius $R_A$ decreases from a value larger than the corotation radius to one which is smaller. In this transistion the 'propeller' goes from being "on" to being "off." The ratio of the spin-down to spin-up torque (or the ratio for the reverse change) in a jump is shown to be of order unity.
doi:10.1086/306945 fatcat:654f2bfadjcjrfd322yk5g7evm