Fast Reconnection in a Two-Stage Process

Abstract

Magnetic reconnection plays an essential role in the generation and evolution of astrophysical magnetic fields. The best tested and most robust reconnection theory is that of Parker and Sweet. According to this theory, the reconnection rate scales with magnetic diffusivity lambda as lambda^0.5. In the interstellar medium, the Parker-Sweet reconnection rate is far too slow to be of interest. Thus, a mechanism for fast reconnection seems to be required. We have studied the magnetic merging of two oppositely directed flux systems in weakly ionized, but highly conducting, compressible gas. In such systems, ambipolar diffusion steepens the magnetic profile, leading to a thin current sheet. If the ion pressure is small enough, and the recombination of ions is fast enough, the resulting rate of magnetic merging is fast, and independent of lambda. Slow recombination or sufficiently large ion pressure leads to slower merging which scales with lambda as lambda^0.5. We derive a criterion for distinguishing these two regimes, and discuss applications to the weakly ionized ISM and to protoplanetary accretion disks.

21 pages, 13 figures, submitted to ApJ

References in corpus (4)

• Gravitational Collapse in Turbulent Molecular Clouds. I. Gasdynamical Turbulence
• Magnetic Reconnection: Sweet-Parker Versus Petschek
• A Numerical Simulation of the Reconnection Layer in 2D Resistive MHD
• Rate of steady-state reconnection in an incompressible plasma

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