Three-dimensional relativistic magnetohydrodynamic simulations of the kelvin-helmholtz instability: Magnetic field amplification by a turbulent dynamo

Weiqun Zhang, Andrew MacFadyen, Peng Wang

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Magnetic field strengths inferred for relativistic outflows including gamma-ray bursts (GRBs) and active galactic nuclei are larger than naively expected by orders of magnitude. We present three-dimensional relativistic magnetohydrodynamic simulations demonstrating amplification and saturation of a magnetic field by a macroscopic turbulent dynamo triggered by the Kelvin-Helmholtz shear instability. We find rapid growth of electromagnetic energy due to the stretching and folding of field lines in the turbulent velocity field resulting from nonlinear development of the instability. Using conditions relevant for GRB internal shocks and late phases of GRB afterglow, we obtain amplification of the electromagnetic energy fraction to εB 5 × 10-3. This value decays slowly after the shear is dissipated and appears to be largely independent of the initial field strength. The conditions required for operation of the dynamo are the presence of velocity shear and some seed magnetization both of which are expected to be commonplace. We also find that the turbulent kinetic energy spectrum for the case studied obeys Kolmogorov's 5/3 law and that the electromagnetic energy spectrum is essentially flat with the bulk of the electromagnetic energy at small scales.

    Original languageEnglish (US)
    Pages (from-to)L40-L44
    JournalAstrophysical Journal
    Volume692
    Issue number1
    DOIs
    StatePublished - 2009

    Keywords

    • Gamma rays: bursts
    • Instabilities
    • MHD
    • Magnetic fields
    • Methods: numerical
    • Relativity
    • Turbulence

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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