The critical role of magnetic helicity in astrophysical large-scale dynamos

TL;DR

This paper reviews how magnetic helicity influences large-scale astrophysical dynamos, affecting energy redistribution, decay, and saturation processes, with implications for solar magnetic activity.

Contribution

It provides a comparative analysis of magnetic helicity's role in dynamo behavior with and without energy supply, highlighting fluxes' impact on dynamo saturation and decay.

Findings

Magnetic energy redistributes to larger scales in both dynamo and decay cases.

Magnetic helicity fluxes can accelerate the decay of helical fields.

Saturation of helical dynamos can be hastened by magnetic helicity fluxes.

Abstract

The role of magnetic helicity in astrophysical large-scale dynamos is reviewed and compared with cases where there is no energy supply and an initial magnetic field can only decay. In both cases magnetic energy tends to get redistributed to larger scales. Depending on the efficiency of magnetic helicity fluxes, the decay of a helical field can speed up. Likewise, the saturation of a helical dynamo can speed up through magnetic helicity fluxes. The astrophysical importance of these processes is reviewed in the context of the solar dynamo and an estimated upper limit for the magnetic helicity flux of 10^46 Mx^2/cycle is given.