Model of Reconnection of Weakly Stochastic Magnetic Field and its Testing

TL;DR

This paper tests a model of magnetic reconnection in turbulent astrophysical fluids, demonstrating that turbulence alone can enable fast reconnection rates regardless of microphysical plasma effects.

Contribution

The paper provides numerical validation of the Lazarian & Vishniac (1999) model, showing turbulence-driven fast reconnection in weakly stochastic magnetic fields.

Findings

Reconnection rate depends on magnetic field stochasticity and turbulence scale.

Reconnection can be fast without anomalous plasma effects.

Numerical simulations confirm the model's predictions.

Abstract

Astrophysical fluids are generically turbulent, which means that frozen-in magnetic fields are, at least, weakly stochastic. Therefore realistic studies of astrophysical magnetic reconnection should include the effects of stochastic magnetic field. In the paper we discuss and test numerically the Lazarian & Vishniac (1999) model of magnetic field reconnection of weakly stochastic fields. The turbulence in the model is assumed to be subAlfvenic, with the magnetic field only slightly perturbed. The model predicts that the degree of magnetic field stochasticity controls the reconnection rate and that the reconnection can be fast independently on the presence or absence of anomalous plasma effects. For testing of the model we use 3D MHD simulations. To measure the reconnection rate we employ both the inflow of magnetic flux and a more sophisticated measure that we introduce in the paper. Both measures of reconnection provide consistent results. Our testing successfully reproduces the dependences predicted by the model, including the variations of the reconnection speed with the variations of the injection scale of turbulence driving as well as the intensity of driving. We conclude that, while anomalous and Hall-MHD effects in particular circumstances may be important for the initiation of reconnection, the generic astrophysical reconnection is fast due to turbulence, irrespectively of the microphysical plasma effects involved. This conclusion justifies numerical modeling of many astrophysical environments, e.g. interstellar medium, for which plasma-effect-based collisionless reconnection is not applicable.