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

Stepanovs, Deniss; Fendt, Christian; Sheikhnezami, Somayeh

doi:10.1088/0004-637X/796/1/29

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

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Abstract

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 outflowsmore »« less

Authors:

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

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

Publication Date:: Thu Nov 20 00:00:00 EST 2014

OSTI Identifier:: 22370201

Resource Type:: Journal Article

Journal Name:: Astrophysical Journal

Additional Journal Information:: Journal Volume: 796; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X

Country of Publication:: United States

Language:: English

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

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                    Stepanovs, Deniss, Fendt, Christian, and Sheikhnezami, Somayeh. Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo.  United States: N. p., 2014. 
        Web.  doi:10.1088/0004-637X/796/1/29.

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                    Stepanovs, Deniss, Fendt, Christian, & Sheikhnezami, Somayeh. Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo.  United States.  https://doi.org/10.1088/0004-637X/796/1/29

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                    Stepanovs, Deniss, Fendt, Christian, and Sheikhnezami, Somayeh. 2014.  
        "Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo".  United States.  https://doi.org/10.1088/0004-637X/796/1/29.

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@article{osti_22370201,

  title        = {Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo},

  author       = {Stepanovs, Deniss and Fendt, Christian and Sheikhnezami, Somayeh},

  abstractNote = {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.},

  doi          = {10.1088/0004-637X/796/1/29},

  url          = {https://www.osti.gov/biblio/22370201},
  journal      = {Astrophysical Journal},

  issn         = {0004-637X},

  number       = 1,

  volume       = 796,

  place        = {United States},

  year         = {Thu Nov 20 00:00:00 EST 2014},

  month        = {Thu Nov 20 00:00:00 EST 2014}

}

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