Strongly magnetized accretion disks around black holes Bhupendra - - PowerPoint PPT Presentation

Strongly magnetized accretion disks around black holes

Bhupendra Mishra

JILA, University of Colorado Boulder Collaborators: Jake Simon, Phil Armitage and Mitch Begelman

Types of Accretion disks

Geometrically:

Thin disk Thick disk Slim disk

• Cold, close to sub-Eddington, optically thick

Cold, Eddington or super-Eddington, optically thick, advection dominated

• Optically thin, advection dominated

Shakura & Sunyaev 1973, Novikov & Thorne 1973, Lynden-Bell & Pringle 1974 Katz 1977, Begelman 1979, Begelman & Meier 1982, Abramowicz et al. 1988 Abramowicz, Jaroszynski, Sikora 1978, Narayan & Yi 1994 BH BH BH Thin Slim Thick

Geometrically thin disks

H/r ⌧ 1

Radiatively efficient

BH Shakura & Sunyaev 1973 BM+ 2016

Prad Pgas

BH

α = < Trφ > < Pgas >

Instabilities

Thermal Instability Viscous Instability

Hydrodynamical:

BM+ 2016

Local simulations

Jiang et al. 2013

Global simulation

Unstable branch S t a b l e b r a n c h R = 10 M , α = 0.02 t0 tf Prad >> Pgas Pgas > > Prad

BM+ 2016

Open Questions

• Why do we find thermally unstable disks in simulations ?

What can stabilize them ? Perhaps magnetic field (Sàdowski 2016)

• What are effects of net vertical magnetic field in global

simulations?

• Can we learn something about AGN accretion ?

weakly magnetized strongly magnetized magnetically arrested βp> 105 βp~ 102 βp< 1 βt ~ 102 βt < 1 MRI active MRI active MRI suppressed increasing poloidal magnetic flux

Sketch: Phil Armitage

Local simulations

Salvesen et al. 2016 50 100 150 200

Global simulations

Zhu & Stone 2018

Initial setup

ρ0(R, z = 0) = ρ0(R0, z = 0) ✓ R R0 ◆q

ρ(R, z) = ρ(R, z = 0)exp GM c2

s

✓ 1 √ R2 + z2 − 1 R ◆

vφ(R, z) = vK " (p + q) ✓ cs vφ,k ◆2 + 1 + q − qR √ R2 + z2 #1/2

Mass Density

Static mesh refinement

Magnetically elevated disks

βi = 100 βi = 300 βi = 1000

Elevated Accretion

Bφ

ρvr

Turbulent viscosity

Spiral structures

βi = 100 βi = 300

βi = 1000

Spiral structures

• Accretion disks get elevated and inflow occurs in

higher altitudes

• Qualitative agreement with local shearing box

simulations

• Logarithmic spiral structures
• Future work: include radiative transfer

Conclusions

Thank you