Global 3D MHD Simulations of Dynamo Effects Lia Hankla University - - PowerPoint PPT Presentation

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Global 3D MHD Simulations of Dynamo Effects Lia Hankla University - - PowerPoint PPT Presentation

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Global 3D MHD Simulations of Dynamo Effects Lia Hankla University of Colorado, Boulder Bhupendra Mishra, Jake Simon, Mitch Begelman, Phil Armitage 1 Black Hole Binary State Transitions First discovered: Cygnus X-1 Usually: X-ray burst,

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SLIDE 1

Global 3D MHD Simulations

  • f Dynamo Effects

Lia Hankla University of Colorado, Boulder

Bhupendra Mishra, Jake Simon, Mitch Begelman, Phil Armitage

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SLIDE 2

Black Hole Binary State Transitions

  • First discovered: Cygnus X-1
  • Usually: X-ray burst, then fade, can
  • bserve companion
  • Now have > 20 systems1

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Lia Hankla, Athena++ Workshop March 2019

1Remillard & McClintock 2006

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SLIDE 3

Transition Hysteresis

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Quiescent state: Dim (L≈1030.5 erg/s), Γ=1.5-2.1, Thick disk Hard state: Jets, Γ=1.4-2.1 Thermal (high/soft) state: Thin disk

Lia Hankla, Athena++ Workshop March 2019

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SLIDE 4

Model for Hysteresis Mechanism

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  • Flux accumulates
  • Thick-to-thin disk

transition

  • Flux diffuses out
  • f thin disk
  • Thick disk

reforms, flux loop develops, footpoints advect/diffuse

Lia Hankla, Athena++ Workshop March 2019

Begelman & Armitage 2014, Fig. 1

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SLIDE 5

Model for Hysteresis Mechanism

  • Flux accumulates
  • Thick-to-thin disk

transition

  • Flux diffuses out
  • f thin disk
  • Thick disk

reforms, flux loop develops, footpoints advect/diffuse

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Lia Hankla, Athena++ Workshop March 2019

Begelman & Armitage 2014, Fig. 1

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SLIDE 6

How does the magnetic field in thin disks behave?

Driving Questions

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Diffusion/advection

  • Conditions
  • Lubow, Papaloizou, Pringle 1994
  • Guilet & Ogilvie 2012, 2013
  • Liska et. al. 2018b

Regeneration

  • Dynamo mechanisms
  • Global or local?
  • Saturation level?
  • Generic?
  • Lead to transition to thick disk?

Lia Hankla, Athena++ Workshop March 2019

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SLIDE 7

Status of the Large-Scale Dynamo

Toroidal Poloidal Vertical

Lia Hankla, Athena++ Workshop March 2019

Thin Thick Beckwith et. al. 2008 Liska et. al. 2018a Beckwith et. al. 2011 Fromang & Nelson 2006 Beckwith et. al. 2008 Liska et. al. 2018b Hogg & Reynolds 2018 Zhu & Stone 2018 McKinney et. al. 2012 McKinney et. al. 2012 Fragile & Sadowski 2017

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SLIDE 8

Status of the Large-Scale Dynamo

Toroidal Poloidal Vertical

Lia Hankla, Athena++ Workshop March 2019

Thin Thick Beckwith et. al. 2008 Liska et. al. 2018a Beckwith et. al. 2011 Fromang & Nelson 2006 Beckwith et. al. 2008 Liska et. al. 2018b Hogg & Reynolds 2018 Zhu & Stone 2018 McKinney et. al. 2012 McKinney et. al. 2012 Fragile & Sadowski 2017

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SLIDE 9

Status of the Large-Scale Dynamo

Toroidal Poloidal Vertical

Lia Hankla, Athena++ Workshop March 2019

Thin Thick Beckwith et. al. 2008 Liska et. al. 2018a Beckwith et. al. 2011 Fromang & Nelson 2006 Beckwith et. al. 2008 Liska et. al. 2018b Hogg & Reynolds 2018 Zhu & Stone 2018 McKinney et. al. 2012 McKinney et. al. 2012 Fragile & Sadowski 2017

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SLIDE 10

Set-up

  • Global, ideal MHD,

pseudo-Newtonian potential

  • H/R = 0.05,

hydrostatic equilibrium

  • Two toroidal flux

tubes: zero net flux, <𝛾min>=103

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Lia Hankla, Athena++ Workshop March 2019

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SLIDE 11

Next Steps

  • Ensure the MRI is resolved: both toroidal and poloidal! Necessary condition:

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Lia Hankla, Athena++ Workshop March 2019

May push to stronger magnetic fields

  • Run, run at different

resolutions, analyze

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SLIDE 12

Summary

  • Under what conditions is poloidal flux generated from toroidal flux?
  • Is the dynamo process global or local? Compare to local simulations

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Lia Hankla, Athena++ Workshop March 2019

Questions?