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, then fade, can ● observe companion Now have > 20 systems 1 ● 1 Remillard & McClintock 2006 Lia Hankla, Athena++ Workshop March 2019 2
Transition Hysteresis Thermal (high/soft) state: Thin disk Hard state: Jets, Γ=1.4-2.1 Quiescent state: Dim (L≈10 30.5 erg/s), Γ=1.5-2.1, Thick disk Lia Hankla, Athena++ Workshop March 2019 3
Model for Hysteresis Mechanism ● Flux accumulates Thick-to-thin disk ● transition ● Flux diffuses out of thin disk Thick disk ● reforms, flux loop develops, footpoints advect/diffuse Lia Hankla, Athena++ Workshop March 2019 Begelman & Armitage 2014, Fig. 1 4
Model for Hysteresis Mechanism ● Flux accumulates Thick-to-thin disk ● transition ● Flux diffuses out of thin disk Thick disk ● reforms, flux loop develops, footpoints advect/diffuse Lia Hankla, Athena++ Workshop March 2019 Begelman & Armitage 2014, Fig. 1 5
Driving Questions Diffusion/advection -Conditions -Lubow, Papaloizou, Pringle 1994 -Guilet & Ogilvie 2012, 2013 How does the magnetic -Liska et. al. 2018b field in thin disks behave? Regeneration -Dynamo mechanisms -Global or local? -Saturation level? -Generic? -Lead to transition to thick disk? Lia Hankla, Athena++ Workshop March 2019 6
Status of the Large-Scale Dynamo Toroidal Poloidal Vertical Thick McKinney et. al. 2012 McKinney et. al. 2012 Beckwith et. al. 2008 Beckwith et. al. 2008 Liska et. al. 2018a Fragile & Sadowski 2017 Hogg & Reynolds 2018 Beckwith et. al. 2011 Fromang & Nelson 2006 Liska et. al. 2018b Zhu & Stone 2018 Thin Lia Hankla, Athena++ Workshop March 2019
Status of the Large-Scale Dynamo Toroidal Poloidal Vertical Thick McKinney et. al. 2012 McKinney et. al. 2012 Beckwith et. al. 2008 Beckwith et. al. 2008 Liska et. al. 2018a Fragile & Sadowski 2017 Hogg & Reynolds 2018 Beckwith et. al. 2011 Fromang & Nelson 2006 Liska et. al. 2018b Zhu & Stone 2018 Thin Lia Hankla, Athena++ Workshop March 2019
Status of the Large-Scale Dynamo Toroidal Poloidal Vertical Thick McKinney et. al. 2012 McKinney et. al. 2012 Beckwith et. al. 2008 Beckwith et. al. 2008 Liska et. al. 2018a Fragile & Sadowski 2017 Hogg & Reynolds 2018 Beckwith et. al. 2011 Fromang & Nelson 2006 Liska et. al. 2018b Zhu & Stone 2018 Thin Lia Hankla, Athena++ Workshop March 2019
Set-up ● Global, ideal MHD, pseudo-Newtonian potential ● H/R = 0.05, hydrostatic equilibrium ● Two toroidal flux tubes: zero net flux, < 𝛾 min >=10 3 Lia Hankla, Athena++ Workshop March 2019 10
Next Steps ● Ensure the MRI is resolved: both toroidal and poloidal! Necessary condition: May push to stronger magnetic fields ● Run, run at different resolutions, analyze Lia Hankla, Athena++ Workshop March 2019 11
Summary ● Under what conditions is poloidal flux generated from toroidal flux? Is the dynamo process global or local? Compare to local simulations ● Questions? Lia Hankla, Athena++ Workshop March 2019 12
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