turbulence in protoplanetary disks · 2019. 3. 21. · summary ¥ protoplanetary disks are likely...
TRANSCRIPT
Jacob B. Simon
June 12, 2012Origins of Stars and Their
Planetary Systems
Turbulence in Protoplanetary Disks
CollaboratorsPhil ArmitageKris Beckwith
Meredith HughesJim Stone
Xuening Bai
JILA Postdoctoral FellowUniversity of Colorado
Courtesy: NASA
Defining the Environment for Planet Formation
Friday, 10 August, 12
We can actually see these systems
Courtesy: NASA
HH30 HD 163296
Hughes et al. (2011)
Friday, 10 August, 12
Dept of Earth & Planetary Sciences, KOBE University
• Dust coagulation is the very earliest stage in planet formation
• Well understood processes involving radial drift and vertical settling in a laminar disk
• But these disks are turbulent
• Global gas evolution will set the conditions for planet formation at various radii
• Turbulence stirs up not only dust, but has importance for mixing of all pre-planetary bodies
Friday, 10 August, 12
Disk turbulence is intimately tied to angular momentum transport
Mass
Angular momentum
Friday, 10 August, 12
Disk turbulence is intimately tied to angular momentum transport
Mass
Angular momentum
• Microphysical viscosity is way too small to transport angular momentum.
Friday, 10 August, 12
Disk turbulence is intimately tied to angular momentum transport
Mass
• Shakura and Sunyaev (1973) suggested turbulent angular momentum transport.
Angular momentum
• Microphysical viscosity is way too small to transport angular momentum.
Turbulent stresses
Friday, 10 August, 12
Our primary goal is to analyze protoplanetary disk turbulence from first principles and study its influence on the very earliest stages of planet formation
Friday, 10 August, 12
Three likely sources of turbulence
John Hawley
Magnetorotational Instability (MRI)
Kratter et al. (2010)
Self-gravitySubcritical Baroclinic Instability
Hubert Klahr
Friday, 10 August, 12
Three likely sources of turbulence
John Hawley
Magnetorotational Instability (MRI)
Kratter et al. (2010)
Self-gravitySubcritical Baroclinic Instability
Hubert Klahr
Needs particular radial entropy profile. Still some
debate about its relevance in low-mass irradiated disks.
Friday, 10 August, 12
Three likely sources of turbulence
John Hawley
Magnetorotational Instability (MRI)
Kratter et al. (2010)
Self-gravitySubcritical Baroclinic Instability
Hubert Klahr
Needs particular radial entropy profile. Still some
debate about its relevance in low-mass irradiated disks.
Important early on or for very massive disks.
Friday, 10 August, 12
Three likely sources of turbulence
John Hawley
Magnetorotational Instability (MRI)
Kratter et al. (2010)
Self-gravitySubcritical Baroclinic Instability
Hubert Klahr
Needs particular radial entropy profile. Still some
debate about its relevance in low-mass irradiated disks.
Important early on or for very massive disks.
Very likely candidate, but requires sufficient disk
ionization levels
Friday, 10 August, 12
Three likely sources of turbulence
John Hawley
Magnetorotational Instability (MRI)
Kratter et al. (2010)
Self-gravitySubcritical Baroclinic Instability
Hubert Klahr
Needs particular radial entropy profile. Still some
debate about its relevance in low-mass irradiated disks.
Important early on or for very massive disks.
Very likely candidate, but requires sufficient disk
ionization levels
Most relevant for our studies
Friday, 10 August, 12
Hawley (2000)
A weak magnetic field destabilizes orbiting gas: the magnetorotational instability (MRI)
Friday, 10 August, 12
Hawley (2000)
A weak magnetic field destabilizes orbiting gas: the magnetorotational instability (MRI)
Friday, 10 August, 12
Low ionization levels enhance non-ideal magnetohydrodynamic (MHD) effects
Three effects
1. Ohmic resistivity
2. Hall effect
3. Ambipolar diffusion
e-
ion+ collide with neutrals
e-
ion+ collide with neutralstied to mag. field
e-
ion+tied to mag. field
Friday, 10 August, 12
Low ionization levels enhance non-ideal magnetohydrodynamic (MHD) effects
Armitage (2011)
- Hall effect is important but not on the second image.- Explain each non-ideal term
Friday, 10 August, 12
Low ionization levels enhance non-ideal magnetohydrodynamic (MHD) effects
Armitage (2011)
- Hall effect is important but not on the second image.- Explain each non-ideal term
Friday, 10 August, 12
Our Goals
Friday, 10 August, 12
Our Goals
Our primary goal is to analyze protoplanetary disk turbulence from first principles and study its influence on the very earliest stages of planet formation
Friday, 10 August, 12
Our Goals• To develop high resolution, numerically converged disk simulations that span the range of physical conditions in protoplanetary disks
• To compute observable signatures from this turbulence to constrain theoretical models, particularly the dead zone model
• To study the interaction of turbulence with dust particles for use in planetesimal formation models.
Friday, 10 August, 12
Our Goals• To develop high resolution, numerically converged disk simulations that span the range of physical conditions in protoplanetary disks
• To compute observable signatures from this turbulence to constrain theoretical models, particularly the dead zone model
• To study the interaction of turbulence with dust particles for use in planetesimal formation models.
Friday, 10 August, 12
Local simulations: examine small co-rotating disk patch
• Assume Cartesian geometry• Add appropriate source terms• Solve equations of MHD• Shearing periodic boundaries• Valid if H/R << 1• Assume gas is isothermalx
y
z
Friday, 10 August, 12
Local simulations: examine small co-rotating disk patch
• Assume Cartesian geometry• Add appropriate source terms• Solve equations of MHD• Shearing periodic boundaries• Valid if H/R << 1• Assume gas is isothermalx
y
z
Friday, 10 August, 12
A state-of-the-art MHD code
Athena
See Stone et al. (2008) for code details
Friday, 10 August, 12
We use a minimum-mass solar nebula model and calculate the Ohmic resistivity at all
radii and heights
Armitage (2011)
Friday, 10 August, 12
Armitage (2011)
Focus on different radial regions
< 0.1 AU
4 AU
10 AU
50 AU
Friday, 10 August, 12
First, let’s consider the limit of ideal MHD
Friday, 10 August, 12
First, let’s consider the limit of ideal MHD
Armitage (2011)
< 0.1 AU
Friday, 10 August, 12
First, let’s consider the limit of ideal MHD
But this limit is also useful as a starting point before adding in more complex physics.
Friday, 10 August, 12
Vary the local domain size
0.5H x 2H x 8H2H x 4H x 8H
4H x 8H x 8H
Friday, 10 August, 12
8H x 16H x 8H
Vary the local domain size
4H x 8H x 8H
Friday, 10 August, 12
8H x 16H x 8H
Vary the local domain size
Friday, 10 August, 12
8H x 16H x 8H
Vary the local domain size
16H x 32H x 8HFriday, 10 August, 12
Vary the local domain size
0.5H x 2H x 8H
16H x 32H x 8HFriday, 10 August, 12
Simon, Beckwith, Armitage (2012)
Results: Ideal MHD and the importance of different length scales
8Hx16Hx8H 16Hx32Hx8H
4Hx8Hx8H2Hx4Hx8H
Friday, 10 August, 12
• These zonal flows may have a scale of ~10H.
• Must determine if they exist in global simulations or are an artifact of local simulations!
Friday, 10 August, 12
Armitage (2011)
Step up complexity by adding in Ohmic resistivity and consider multiple radii
4 AU
10 AU
50 AU
All boxes are 4Hx8Hx8H
box sizes limited to intermediate size due to finite resources
Friday, 10 August, 12
Results: Turbulent velocity distribution
Simon, Armitage, Beckwith (2011)
vertical
horizontalThis is very similar to the ideal MHD distribution for the largest box
Friday, 10 August, 12
Results: Turbulent velocity distribution
vertical
horizontal
Simon, Armitage, Beckwith (2011)
Friday, 10 August, 12
Our turbulent velocities roughly agree with observed measurements
Hughes et al. (2011) probed surface layers in outer disk: |v|/cs ~ 0.4 for HD 163296 |v|/cs < 0.1 for TW Hya
Our results so far suggest |v|/cs ~ 0.1-1
Friday, 10 August, 12
Next
Friday, 10 August, 12
Next
• Continue to improve physics - add in ambipolar diffusion and Hall effect
Friday, 10 August, 12
Next
• Continue to improve physics - add in ambipolar diffusion and Hall effect
• Simultaneously collaborate with observers to make a more direct comparison between our models and their observations - create synthetic observations (already in progess)
Friday, 10 August, 12
Next
• Continue to improve physics - add in ambipolar diffusion and Hall effect
• Simultaneously collaborate with observers to make a more direct comparison between our models and their observations - create synthetic observations (already in progess)
• Calculate interaction of turbulence with dust particles to determine mixing, diffusion, concentration, etc.
Friday, 10 August, 12
Summary
• Protoplanetary disks are likely not quiescent, but turbulent due to the MRI.
• This turbulence generates long-lived ~10 H structures in the density field, which could be important for particle trapping.
• Calculations of the turbulent velocity distribution roughly agree with observations.
• We will continue a first principles approach to studying planet formation in these disks while simultaneously comparing with observations.
Friday, 10 August, 12
Extra slides
Friday, 10 August, 12
We utilize powerful supercomputers to run these simulations
Friday, 10 August, 12
We utilize powerful supercomputers to run these simulations
Friday, 10 August, 12
Friday, 10 August, 12
There are new sub-mm observations from which turbulent velocities can be inferred.
Hughes et al. (2011)
Friday, 10 August, 12
There are new sub-mm observations from which turbulent velocities can be inferred.
Hughes et al. (2011)
Friday, 10 August, 12