Launching of Jets by Propeller Mechanism

TL;DR

This study uses axisymmetric simulations to explore how rapidly rotating magnetized stars in the propeller regime can generate outflows, revealing conditions for weak and strong outflows and their impact on star spin-down.

Contribution

It demonstrates that outflows occur only with sufficient disk-magnetosphere friction and accretion flux, highlighting the conditions for strong propeller-driven winds and their effects.

Findings

Outflows occur only with high disk-magnetosphere friction.

Strong outflows are magneto-centrifugally ejected from the disk.

Stars spin down rapidly due to magnetic interactions.

Abstract

We carried out axisymmetric simulations of disk accretion to a rapidly rotating magnetized star in the "propeller" regime. Simulations show that propellers may be "weak" (with no outflows), and "strong" (with outflows). Investigation of the difference between these two regimes have shown that outflows appear only in the case where the "friction" between the disk and magnetosphere is sufficiently large, and when accreting matter flux is not very small. Matter outflows in a wide cone and is magneto-centrifugally ejected from the inner regions of the disk. Closer to the axis there is a strong, collimated, magnetically dominated outflow of energy and angular momentum carried by the open magnetic field lines from the star. The "efficiency" of the propeller may be very high in the respect that most of the incoming disk matter is expelled from the system in winds. The star spins-down rapidly due to the magnetic interaction with the disk through closed field lines and with corona through open field lines. This mechanism may act in a variety of situations where magnetized star rotates with super-Keplerian velocity at the magnetospheric boundary. We speculate that in general any object rotating with super-Keplerian velocity may drive outflows from accreting disk, if the friction between them is sufficiently large.