LOCAL TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS OF THE COLLISIONLESS MAGNETOROTATIONAL INSTABILITY

Journal Article · Fri Aug 10 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/755/1/50· OSTI ID:22039151

Riquelme, Mario A; Quataert, Eliot ^[1]; Sharma, Prateek ^[2]; Spitkovsky, Anatoly ^[3]

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1. Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, CA 94720 (United States)
2. Department of Physics, Indian Institute of Science, Banglore 560012 (India)
3. Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States)

The magnetorotational instability (MRI) is a crucial mechanism of angular momentum transport in a variety of astrophysical accretion disks. In systems accreting at well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the disk is essentially collisionless. We present a nonlinear study of the collisionless MRI using first-principles particle-in-cell plasma simulations. We focus on local two-dimensional (axisymmetric) simulations, deferring more realistic three-dimensional simulations to future work. For simulations with net vertical magnetic flux, the MRI continuously amplifies the magnetic field, B, until the Alfven velocity, v{sub A} , is comparable to the speed of light, c (independent of the initial value of v{sub A} /c). This is consistent with the lack of saturation of MRI channel modes in analogous axisymmetric MHD simulations. The amplification of the magnetic field by the MRI generates a significant pressure anisotropy in the plasma (with the pressure perpendicular to B being larger than the parallel pressure). We find that this pressure anisotropy in turn excites mirror modes and that the volume-averaged pressure anisotropy remains near the threshold for mirror mode excitation. Particle energization is due to both reconnection and viscous heating associated with the pressure anisotropy. Reconnection produces a distinctive power-law component in the energy distribution function of the particles, indicating the likelihood of non-thermal ion and electron acceleration in collisionless accretion disks. This has important implications for interpreting the observed emission-from the radio to the gamma-rays-of systems such as Sgr A*.

• OSTI ID: 22039151
• Journal Information: Astrophysical Journal, Vol. 755, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCELERATION
ACCRETION DISKS
ANISOTROPY
ASTRONOMY
ASTROPHYSICS
AXIAL SYMMETRY
BLACK HOLES
COSMIC ELECTRONS
ENERGY SPECTRA
GAMMA RADIATION
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
MILKY WAY
NMR IMAGING
PLASMA INSTABILITY
PLASMA SIMULATION
TWO-DIMENSIONAL CALCULATIONS