Generation of Magnetic Field by Combined Action of Turbulence and Shear

TL;DR

This paper demonstrates through numerical simulations that nonhelical turbulence combined with linear shear can generate large-scale magnetic fields via a shear dynamo effect, which may be common in astrophysical systems.

Contribution

The study reveals a new shear dynamo mechanism producing large-scale magnetic fields in nonhelical turbulence with shear, characterized by specific scale and growth rate dependencies.

Findings

Magnetic fields grow exponentially at scales larger than turbulence.

The characteristic magnetic scale scales as S^{-1/2}.

Growth rate is proportional to the shearing rate S.

Abstract

The feasibility of a mean-field dynamo in nonhelical turbulence with superimposed linear shear is studied numerically in elongated shearing boxes. Exponential growth of magnetic field at scales much larger than the outer scale of the turbulence is found. The charateristic scale of the field is l_B ~ S^{-1/2} and growth rate is gamma ~ S, where S is the shearing rate. This newly discovered shear dynamo effect potentially represents a very generic mechanism for generating large-scale magnetic fields in a broad class of astrophysical systems with spatially coherent mean flows.