Magnetic Reconnection in Astrophysical Environments

TL;DR

This paper reviews magnetic reconnection in astrophysical environments, emphasizing the role of turbulence in enabling fast reconnection and magnetic field diffusion, challenging traditional flux freezing assumptions and impacting star formation theories.

Contribution

It discusses the Lazarian & Vishniac (1999) turbulent reconnection model, its validation, and implications for magnetic field dynamics and star formation, highlighting turbulence's role in magnetic diffusion.

Findings

Turbulence induces fast magnetic reconnection in 3D astrophysical fluids.

Reconnection rates depend on the level of MHD turbulence, consistent with the Goldreich & Sridhar model.

Magnetic flux freezing does not hold in turbulent fluids, allowing magnetic diffusion.

Abstract

Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turbulence in most astrophysical settings is of pre-existing nature, but it also can be induced by magnetic reconnection itself. In this situation turbulent magnetic field wandering opens up reconnection outflow regions, making reconnection fast. We discuss Lazarian \& Vishniac (1999) model of turbulent reconnection, its numerical and observational testings, as well as its connection to the modern understanding of the Lagrangian properties of turbulent fluids. We show that the predicted dependences of the reconnection rates on the level of MHD turbulence make the generally accepted Goldreich \& Sridhar (1995) model of turbulence self-consistent. Similarly, we argue that the well-known Alfv\'en theorem on flux freezing is not valid for the turbulent fluids and therefore magnetic fields diffuse within turbulent volumes. This is an element of magnetic field dynamics that was not accounted by earlier theories. For instance, the theory of star formation that was developing assuming that it is only the drift of neutrals that can violate the otherwise perfect flux freezing, is affected and we discuss the consequences of the turbulent diffusion of magnetic fields mediated by reconnection.