Planetesimal Formation in Zonal Flows - uni …...Planetesimal Formation in Zonal Flows Karsten...

Planetesimal Formation in Zonal Flows

Karsten Dittrich (PhD student, MPIA Heidelberg)

Hubert Klahr (Supervisor, MPIA Heidelberg)

Anders Johansen (Lund Observatory)

Scales of Planet Formation

Credit: Cornelis Dullemond

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Zonal flows and axisymmetric pressure bumps - Theory

Magnetic pressure

Azimuthal gas velocity

Gas pressure (gas density)

• Magnetic pressure forms large-scale structures

• Orbital shear converts magnetic to kinetic energy

– Zonal flows!

• Geostrophic balance excites axisymmetric pressure bumps

Magnetic pressure

Azimuthal gas velocity

Gas pressure

Magnetic pressure

Azimuthal gas velocity

Gas pressure

www.spitzer.caltech.edu, Johansen & Klahr 2005

Zonal flows in numerical simulations

• View from the top of the disk; integrated over vertical direction

• Snapshot of the gas surface density shows many short-lived high frequency oscillations

Dittrich et al. 2012, submitted

Zonal flows in numerical simulations

• Time-average over 5 orbits reveals radial structure

– Sinusodial radial structure

– About 5 scale heights H

Dittrich et al. 2012, submitted 5H 1.25AU (at 5AU)

Zonal flows in numerical simulations

• Sinusoidal structure has constant width

• Stable for several tens of local orbits

Tim

e

Dittrich et al. 2012, submitted

Zonal flows in numerical simulations

• Life time up to 50 local orbits

• Radial scale of 5 pressure scale heights

Dittrich et al. 2012, submitted

Planetesimal formation in zonal flows

Tim

e

• Radial drift is slowed down by pressure bumps

• Leads to high dust densities

Dittrich et al. 2012, submitted

• All simulations start with a dust-to-gas ratio of 10-2

• Maximal concentrations reached during simulation: – 104 for meter-

sized particles

– Some 100 for decimeter-sized particles

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Particle Size [cm]

Planetesimal formation in zonal flows

Dittrich et al. 2012, submitted

Summary • Zonal flows and the resulting pressure

bumps are a physical feature of magneto-rotationally-unstable protoplanetary disks – Life-time of several tens of local orbits

– Radial size of 5 scale heights (1.25AU at a 5AU orbit); in agreement with global simulations (e.g., Uribe et al. 2011)

• Dust gets trapped at pressure bumps and forms over-densities – Decimeter-sized pebbles can trigger

streaming instability

– Meter-sized boulders can undergo gravitational collapse to form planetesimals

Tim

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Du

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Particle Size [cm]