fast magnetic reconnection events in accretion disks under ...β’4st step: Evaluate the eigenvectors...
Transcript of fast magnetic reconnection events in accretion disks under ...β’4st step: Evaluate the eigenvectors...
Identification of fast magnetic reconnection events in accretion disks under the action of MHD instabilitiesL U Γ S H . S . K A D O WA K I
E L I S A B E T E M . D E G O U V E I A D A L P I N O
J A M E S M . S TO N E
O C TO B E R 1 7 , 2 0 1 7
M A G N E T I C F I E L D S I N T H E U N I V E R S E V I : F R O M L A B O R ATO R Y A N D S TA R S TO T H E P R I M O R D I A L S T R U C T U R E S
Outline
β’ Magnetic reconnection in accretion disk systems
β’ Numerical simulations with a shearing-box approach
β’ MHD instabilities in accretion disks
β’ Identification of fast magnetic reconnection events in the surroundings of accretion disks
β’ Conclusions
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Accretion disk systems
β’ Accretion disks systems are believed to be very common structures in the Universe
β’ These systems are associated to:β’ Black Hole Binaries (BHBs)
β’ Active Galactic Nuclei (AGNs)
β’ Young Stellar Objects (YSOs) and so protoplanetary disks
β’ The formation of a turbulent corona above and below accretion disks plays an important role in magnetic reconnection events
β’ These events could explain the flare emissions in X-ray (YSOs) and in radio and gamma-ray (BHBs and AGNs)
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Turbulent magnetic reconnection in collisional flowsβ’ Lazarian & Vishiniac (1999) model (Kowalβs talk):β’ Reconnection triggered by tubulence
β’ Several reconnection points (at all scales) due to the wandering magnetic field lines
β’ βFastβ reconnection
β’ ππππ β ππ΄ππ΄2
Numerical simulations (Kowal et al. 2009, 2012)
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MHD numerical simulations of accretion disks and coronaMAGNETIC RECONNECTION UNDER THE ACTION OF MHD INSTABILITIES
Aims
β’ The formation of a large scale poloidal magnetic field by the arising of loops due to the Parker-Rayleigh-Taylor instability
β’ The role of Parker-Rayleigh-Taylor and magnetorotationalinstabilities in the formation of a turbulent magnetized corona around accretion disksβ’ Where magnetic reconnection events could occur
β’ The identification of fast magnetic reconnection events by the statistical analysis of the reconnection rate in the corona and disk
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Numerical method (shearing-box)
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Kadowaki (masterβs thesis, 2011)
β’ Shearing-Box (Hawley et al., 1995):β’ A steady flow with a linear shearing velocity:
β’ For a Keplerian disk:
Kadowaki et al. (2017, in prep.)
Numerical method (shearing-box)β’ MHD equations:
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Numerical method (shearing-box)β’ Momentum equation:
Coriolis Force (Radial and Azimuthal components)
Centrifugal + Gravitational Forces (Radial component)
Gravity (Vertical component)
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Numerical method (shearing-box)β’ Boundary Conditions:β’ Computational domain: πΏπ₯, πΏπ¦e πΏπ§
β’ Strictly periodic in all the boundaries at π‘ = 0
β’ The shearing is produced by the slipping of the boundaries in π₯ direction
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Hawley et al. (1995)
MHD instabilitiesMagnetorotational instability (MRI)
β’ A weak magnetic field exerts an elastic force between two fluid elements
β’ This force transfers angular momentum to the outer regionβ’ Making possible the accretion in Keplerian
regimes
β’ Linear regime: Amplification of the magnetic field (dynamo effect)
β’ Non-linear regime: Saturation of the magnetic field and formation of turbulence
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MHD instabilitiesParker-Rayleigh-Taylor instability
β’ Instability driven by strong magnetic fields:
β’ π½ =ππ‘βπππππ
πππππππ‘ππ= 1 (Magnetic buoyance)
β’ Azimuthal magnetic field (β₯ Τ¦π)
β’ Formation of magnetic loops β Magnetic reconnection β Release of energy in the coronal region
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Kadowaki et al. (2017, in prep.)Parker (1966)
Numerical results (Resolution: 2563)β’ Athena code (Stone et al., 2008, 2010)
β’ Model PMRIg_21H_oxyz12
β’ Initial conditions: β’ Isothermal system
β’ Magnetostatic equilibrium
β’ Azimuthal magnetic field (π΅π¦)
β’ π½ = 1.0
β’ Initial Gaussian perturbation in the Keplerian velocity field
β’ Boundaries conditions: β’ π₯: Shearing-periodic
β’ π¦: Periodic
β’ π§: Outflow
β’ 12π» Γ 12π» Γ 12π» (π» = πΆπΞ©β1)
β’ 256π» Γ 256π» Γ 256π» cells
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Numerical results (Resolution: 2563)
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Numerical results (Resolution: 2563)
β’ Transition between PRTI and MRI
β’ Polarity inversions due to the action of the dynamo triggered by MRI
β’ Zero net flux field ( π΅π§ β 0)
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Numerical results (Resolution: 2563)
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Numerical results (Comparison)
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Identification of fast magnetic reconnection events in accretion disksSTATISTICAL ANALYSIS OF THE MAGNETIC RECONNECTION RATE
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 1st step: Sample of cells with π0 > π π» Γ π΅
1 1 2 5 1
1 4 6 4 2
1 3 4 3 1
| π | = 2.6
π
π
In this work, we have used:π = 5
For Ξ΅ = 1
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 2nd step: Sample of cells with local maxima ππππ₯ = ππ΄π π ππ₯Γππ¦Γππ§
1 1 2 5 1
1 4 6 4 2
1 3 4 3 1
ππππ₯ = 6 =ππ΄π π 3Γ3
π
π
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 3st step: Check if the local maxima is between opposite magnetic field polarity
ππππ₯Confirmed!
π
π
π©π
π©π
π©ππ©π
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 3st step: Check if the local maxima is between opposite magnetic field polarity
ππππ₯ Confirmed!
π
π
π©π
π©π
π©ππ©π
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 3st step: Check if the local maxima is between opposite magnetic field polarity
ππππ₯ Rejected!
π
π
π©π
π©π
π©ππ©π
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 4st step: Evaluate the eigenvectors of the Hessian matrix
π» =
ππ₯π₯π ππ₯π¦π ππ₯π§π
ππ¦π₯π ππ¦π¦π ππ¦π§π
ππ§π₯π ππ§π¦π ππ§π§π
π
π
ππ ππβ’ ππ: Indicates the fastest decaying of π (Thickness)
β’ Projection of the magnetic and velocity fields along ππ, ππ and ππ directions
Algorithm
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β’ We have adapted the algorithm of Zhdankin et al. (2013) and extended to a 3D analysis
β’ 5st step: Evaluate the magnetic reconnection rate
ππ
ππ
πππππ΄
=1
2α€
ππ1ππ΄ πππ€ππ
β α€ππ1ππ΄ π’ππππ
ππ΄ =π΅π1
2 + π΅π22 + π΅π3
2
ππππ€ππ
π’ππππ
π <1
2ππππ₯
π <1
2ππππ₯
π >1
2ππππ₯
Similar to Kowal et al. (2009)
Magnetic reconnection rate (Resolution: 2563)
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Upper Corona
Confirmed!Rejected!
Magnetic reconnection rate (Resolution: 2563)
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Upper Corona
Magnetic reconnection rate (Resolution: 2563)
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Magnetic reconnection rate (Resolution: 2563)
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Magnetic reconnection rate (Resolution: 2563)
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Power spectrum (Resolution: 2563)
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t = 1 (Orbits) t = 2 (Orbits)
Power spectrum (Resolution: 2563)
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t = 4 (Orbits) t = 5 (Orbits)
Conclusions
β’ Our simulations have revealed the arising of magnetic loops due to the PRTI followed by the development of turbulence due to PRTI and MRI
β’ Even with an initial high magnetized regime, the disk evolves to a gas-pressure dominant regime with a magnetized coronaβ’ Transport of magnetic field from the disk to the corona by buoyance process
β’ We have evaluated the magnetic reconnection rates and detected the presence of fast magnetic reconnection events, as predicted by the theory of turbulence-induced fast reconnection (Lazarian & Vishiniac, 1999)
β’ The algorithm applied to this work has demonstrated to be an efficient tool for the identification of magnetic reconnection sites in numerical simulations
Kadowaki, de Gouveia Dal Pino & Stone (2017, in prep.)
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Thank you!