Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo

Journal Article · Thu Nov 20 04:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/796/1/29· OSTI ID:22370201

Stepanovs, Deniss; Fendt, Christian; Sheikhnezami, Somayeh ^[1]

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1. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)

We present MHD simulations exploring the launching, acceleration, and collimation of jets and disk winds. The evolution of the disk structure is consistently taken into account. Extending our earlier studies, we now consider the self-generation of the magnetic field by an α{sup 2}Ω mean-field dynamo. The disk magnetization remains on a rather low level, which helps to evolve the simulations for T > 10, 000 dynamical time steps on a domain extending 1500 inner disk radii. We find the magnetic field of the inner disk to be similar to the commonly found open field structure, favoring magneto-centrifugal launching. The outer disk field is highly inclined and predominantly radial. Here, differential rotation induces a strong toroidal component, which plays a key role in outflow launching. These outflows from the outer disk are slower, denser, and less collimated. If the dynamo action is not quenched, magnetic flux is continuously generated, diffuses outward through the disk, and fills the entire disk. We have invented a toy model triggering a time-dependent mean-field dynamo. The duty cycles of this dynamo lead to episodic ejections on similar timescales. When the dynamo is suppressed as the magnetization falls below a critical value, the generation of the outflows and also accretion is inhibited. The general result is that we can steer episodic ejection and large-scale jet knots by a disk-intrinsic dynamo that is time-dependent and regenerates the jet-launching magnetic field.

• OSTI ID: 22370201
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 796; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCELERATION
ACCRETION DISKS
GALAXIES
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETIZATION
MAGNETOHYDRODYNAMICS
MASS TRANSFER
MEAN-FIELD THEORY
ROTATION
SIMULATION
STAR EVOLUTION
STARS
STELLAR WINDS
TIME DEPENDENCE