![Page 1: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/1.jpg)
Growing Magnetic Fields
through Turbulence
Terrence Tricco
Monash Centre for Astrophysics
http://users.monash.edu/~tricco
Daniel Price (Monash)
Christoph Federrath (Monash)
![Page 2: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/2.jpg)
Overview
• Simulations of supersonic magnetised turbulence,
representative of turbulence in the ISM
• Outline:
1) Magnetic fields within star formation
2) Turbulence in the ISM
3) Numerical method and new developments
4) Simulation results
![Page 3: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/3.jpg)
MHD in Star Formation
• Magneto-Rotational Instability in accretion discs
• Provides angular momentum transport out of the
inner disc
Image courtesy of Mark Wardle
![Page 4: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/4.jpg)
MHD in Star Formation
• Jets and Outflows from protostars
Price, Tricco, Bate (2012)
![Page 5: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/5.jpg)
MHD in Star Formation
• Magnetised turbulence in the Interstellar Medium
![Page 6: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/6.jpg)
Turbulence in the ISM
• Pure hydro context:
• Primary role in star formation rate, and efficiency
of gas conversion to stars
• Supersonic turbulence, causes dense filaments
within which star formation occurs
• MHD:
• Small scale dynamo exponentially amplifies
magnetic field
![Page 7: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/7.jpg)
Small Scale Dynamo
• Stretch-Twist-Fold mechanism
amplifies magnetic field on
small scales
• Growth rate determined by
Reynolds and Prandtl numbers
![Page 8: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/8.jpg)
Turbulence Simulations
• Simulation details:
• Mach 10 turbulence
• Isothermal equation of state
• Periodic boundary conditions
• Solenoidal stochastic forcing
• Initially weak magnetic field (Emag 1010 weaker than Ekin)
• Results compared against grid based Flash code
• Extends the pure hydro comparison of Price, Federrath (2010)
![Page 9: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/9.jpg)
Numerical Method: SPH
• Discretise fluid into set of particles which
simulate fluid motion
• Well suited for star formation:
• Couples well with N-body methods
• Strong conservation properties, very stable
• Inherently adaptive, resolution traces mass
• Most difficult numerical aspect of MHD:
![Page 10: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/10.jpg)
Constrained Divergence Cleaning
• Hamiltonian formulation of hyperbolic divergence cleaning
• Ensures energy conservation, guaranteed to always decrease divergence of the field
• Retains conservation and stability properties of SPH
• Accounts for Lagrangian motion of particles
• Approximately 10x decrease in divergence error
Tricco, Price (2012)
![Page 11: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/11.jpg)
Shock Capturing
• Magnetic shocks captured by using Artificial Resistivity
• Resistivity switch activates resistivity only near shocks
• New switch: sets AR
• ie, relative degree of discontinuity in the magnetic field
• Invariant to field strength, captures shocks as field is amplified
Previous switch New switch
![Page 12: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/12.jpg)
Dynamo Amplification
![Page 13: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/13.jpg)
Energy Growth
![Page 14: Growing Magnetic Fields through Turbulencettricco/slides/tricco-anita2013.pdf · of gas conversion to stars •Supersonic turbulence, causes dense filaments within which star formation](https://reader033.vdocuments.mx/reader033/viewer/2022042000/5e6d3fe266665906ec7d2ff9/html5/thumbnails/14.jpg)
Conclusions
• SPH can successfully model dynamo
amplification from supersonic turbulence
• New artificial resistivity switch for magnetic
shock capturing
• Future Goals:
• Simulate MRI with SPH
• Combine MRI + Jets + turbulence
in large cluster simulations