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[73.22] Fast Reconnection in a Two-Stage Process

F. Heitsch (JILA), E.G. Zweibel (JILA/U. Colorado)

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 Sweet and Parker. According to this theory, the reconnection rate scales with magnetic diffusivity \lambda as \lambda^1/2. In the interstellar medium, the Sweet-Parker 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^1/2. We derive a criterion for distinguishing these two regimes, and discuss applications to the weakly ionized ISM and to protostellar accretion disks.

This work was supported in part by the Alexander von Humboldt Society, and NSF Grants AST 9800616 and AST 0098701 to U. Colorado

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.