Planetesimal Formation in Zonal Flows - uni …...Planetesimal Formation in Zonal Flows Karsten...
Transcript of 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
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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
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• 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]