Disk Formation in Magnetized Dense Cores with Turbulence and - - PowerPoint PPT Presentation

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disk formation in magnetized dense cores
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Disk Formation in Magnetized Dense Cores with Turbulence and - - PowerPoint PPT Presentation

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Disk Formation in Magnetized Dense Cores with Turbulence and Ambipolar Diffusion March 21, 2019 Ka Ho (Andy) Lam (University of Virginia) Zhi-Yun Li (UVa) Che-Yu Chen (UVa) Kengo Tomida (OsakaU/Princeton) Bo Zhao (MPE) Credit: Bill Saxton

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March 21, 2019 Ka Ho (Andy) Lam (University of Virginia)

Disk Formation in Magnetized Dense Cores with Turbulence and Ambipolar Diffusion

Zhi-Yun Li (UVa) Che-Yu Chen (UVa) Kengo Tomida (OsakaU/Princeton) Bo Zhao (MPE)

Credit: Bill Saxton (NRAO/AUI/NSF)

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Motivation

  • Provide initial conditions for

protoplanetary disk simulations

  • Large amount of telescope data
  • Young disks with polarization,

e.g., Cox et al. (2018), Kwon et al. (2018)

  • Numerical simulations show that disks

cannot form easily

March 21, 2019 Athena++ Workshop 2019 2

(Cox et al. 2018) DSHARP 1000 AU

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Hydrodynamic Simulation

March 21, 2019 Athena++ Workshop 2019 3

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Magnetic Braking Catastrophe

  • Dust emissions are polarized (on all scales)
  • Grains align to magnetic field lines
  • Hourglass-shaped magnetic field lines
  • Magnetic field interacts strongly with mass

March 21, 2019 Athena++ Workshop 2019 4

Planck BLAST-Pol Li et al. (2014)

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Magnetic Braking Catastrophe

  • Mass-to-flux ratio
  • πœ‡ = 2𝜌 𝐻

𝑁 Ξ¦

  • πœ‡ < 1 β†’ magnetically supported
  • Observationally, πœ‡ ∼ 2

(corrected for geometry)

  • πœ‡ = 2.63 in our simulations

March 21, 2019 Athena++ Workshop 2019 5

Troland & Crutcher (2008)

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Magnetic Braking Catastrophe

  • Ideal MHD simulation
  • B field-induced flattened structure
  • Not rotationally supported
  • Pseudodisk
  • Pinched B field lines causes

magnetic tension torque

  • No rotationally supported disk

March 21, 2019 Athena++ Workshop 2019 6

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Resolutions

  • Magnetic field-rotation misalignment
  • Turbulence
  • Non-ideal MHD effects
  • Ohmic dissipation
  • Hall effect
  • Ambipolar diffusion
  • Non-ideal MHD effects have been studied alone in detail
  • Small disks at early phase, e.g., Vaytet et al. (2018), Tomida et al. (2015)
  • Long-term evolution requires sink particle treatment, e.g., Tomida et al. (2017)

March 21, 2019 Athena++ Workshop 2019 7

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Sink Particle Treatment

  • Gong & Ostriker (2013)
  • Sink particles are created when

conditions are fulfilled

  • Density threshold, minimum of potential, …
  • 3 Γ— 3 Γ— 3 sink regions
  • Excess mass and momentum are put onto

sink particles

  • Magnetic field is untouched
  • Magnetic field decoupled from gas and

accumulate in sink regions

  • Magnetic flux problem: πœ‡βˆ— = 103 βˆ’ 104

March 21, 2019 Athena++ Workshop 2019 8

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Simulation Setup

  • Pseudo-Bonner-Ebert sphere (𝛽 = 0.4)
  • Solid-body rotation (𝛾rot = 0.03)
  • Isothermal EOS (𝑑𝑑 = 0.2 km/s)
  • Turbulence
  • Angular momentum removed globally
  • Mach 0, 0.5, 1
  • Ambipolar diffusivity
  • Assume cosmic-ray ionization-recombination

equilibrium, πœƒA = 𝑅A

𝐢2 4𝜌𝜍3/2

  • 𝑅A = 0.1 Γ—, 0.3 Γ—, 1 Γ—, 3 Γ—, 10 Γ— standard value

(Shu 1992)

  • Evolve to at least 0.2 Mβ˜‰, sometimes 0.3 Mβ˜‰

March 21, 2019 Athena++ Workshop 2019 9

0.5 Mβ˜‰ 5000 AU 4000 AU 256 cells Ξ© = 6 Γ— 10βˆ’13sβˆ’1

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Ideal MHD – Turbulence

March 21, 2019 Athena++ Workshop 2019 10

Laminar Subsonic Transonic

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Ideal MHD – Turbulence

  • Confirm findings in Li et al. (2014)
  • Warped pseudodisk
  • Promote disk formation
  • Proposed mechanisms
  • Earlier leakage of magnetic flux
  • Self-sorting of angular momentum

March 21, 2019 Athena++ Workshop 2019 11

ΰ·€ 𝜍 = 𝑠

cyl𝜍

Ξ£ = 1 Density on cylindrical surface

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March 21, 2019 Athena++ Workshop 2019 12

Ideal MHD Very weak Weak Standard Strong Very strong

Non-ideal MHD – Ambipolar Diffusion (AD)

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 13

Ion Neutral B field line

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 14

Ion Neutral B field line

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 15

Ion Neutral B field line

Magnetic tension

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 16

Ion Neutral B field line

Magnetic tension

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 17

Ion Neutral B field line

Magnetic tension

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 18

Ion Neutral B field line

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 19

Ion Neutral B field line

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 20

Accretion

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 21

Accretion

Accretion-induced strong pinching

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 22

Accretion

Ions experience strong magnetic forces

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 23

Accretion

Less pinching β†’ less drift

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 24

Accretion

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 25

Accretion

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 26

Accretion

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Non-ideal MHD – Ambipolar Diffusion (AD)

March 21, 2019 Athena++ Workshop 2019 27

Accretion Magnetic field curvature

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Non-ideal MHD – Ambipolar Diffusion (AD)

  • As in other studies
  • AD shock (Li & Mckee 1996) or magnetic field plateau (Masson et al. 2016)
  • AD does not guarantee disk formation
  • Strong AD is needed (β‰₯ standard level of AD)
  • Reduced magnetic field strength near the forming stars and in the disks
  • Reduced magnetic braking
  • But reduced magnetic field

strength does not explain reduced torque completely

  • Straighter B field lines

March 21, 2019 Athena++ Workshop 2019 28

Time

Vertical magnetic field strength

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Disk Formation with Turbulence and AD

March 21, 2019 Athena++ Workshop 2019 29

Ideal MHD Very Weak Weak Standard Strong Very strong Ideal MHD Very Weak Weak Standard Strong Very strong

Laminar Turbulent

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Disk Formation with Turbulence and AD

March 21, 2019 Athena++ Workshop 2019 30

Time AD level Time AD level

Laminar Turbulent

Ideal MHD Very weak Weak Standard Strong Very strong Ideal MHD Very weak Weak Standard Strong Very strong

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Disk Formation with Turbulence and AD

  • Turbulence enables early (transient) disk formation
  • Earlier leakage of magnetic flux
  • Self-sorting of angular momentum
  • Strong AD allows disks to survive
  • Decoupling of magnetic flux
  • Less magnetic field line pinching
  • Turbulence suppresses fragmentation in the strong AD case
  • Asymmetry allow angular momentum transport
  • Strong magnetization
  • 𝛾 < 102 β‰ͺ 105 used in protoplanetary disk simulations

March 21, 2019 Athena++ Workshop 2019 31

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Disk Formation in Athena++

  • Self-gravity with AMR
  • General EOS / radiative transfer
  • Sink particle treatment
  • Turbulence
  • Non-ideal MHD

March 21, 2019 Athena++ Workshop 2019 32

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Summary

  • Implementation of sink particle treatment is needed
  • Turbulence shapes the accretion flow into a warped pseudodisk
  • Turbulence and ambipolar diffusion work in a complementary way
  • Turbulence allow early disk formation
  • Standard or stronger ambipolar diffusion allow disk to survive
  • Disks formed in this study are strongly magnetized

March 21, 2019 Athena++ Workshop 2019 33