Are jets ejected from locally magnetized accretion disks?

Abstract

We investigated the jet formation from accretion disks in which a weak localized poloidal magnetic field is initially embedded. Previous MHD numerical simulations of jet formation from accretion disks initially assumed a large-scale vertical uniform magnetic field that threads the disk, which showed that jets are ejected from accretion disks by a magneto-centrifugal force and magnetic pressure. In contrast to a large-scale uniform magnetic field, what happens if the magnetic field is localized in the disk? Our MHD numerical simulation shows that the jet structure appears even if the initial magnetic field is localized in the disk. The disk material is ejected as a poloidal magnetic loop by magnetic pressure due to a toroidal magnetic field that is generated by the disk rotation. Though the ejection mechanism is different from that of the magneto-centrifugally driven jet model, the rising magnetic loop behaves like a jet; it is collimated by a pinching force of the toroidal magnetic field, and its velocity is on order of the Keplerian velocity of the disk.