First-Principles Theory of the Relativistic Magnetic Reconnection Rate in Astrophysical Pair Plasmas

TL;DR

This paper presents a first-principles analytical model for the relativistic magnetic reconnection rate in strongly magnetized pair plasmas, explaining how magnetic field collapse leads to fast reconnection in astrophysical environments.

Contribution

It introduces a novel theoretical framework based on energy and current considerations, elucidating the physics behind fast reconnection in relativistic pair plasmas.

Findings

Thermal pressure at the x-line is much lower than upstream magnetic pressure.

Magnetic field lines collapse inward, creating an open outflow geometry.

The model aligns with kinetic simulation results and explains fast reconnection phenomena.

Abstract

We develop a first-principles model for the relativistic magnetic reconnection rate in strongly magnetized pair plasmas. By considering the energy budget and required current density near the x-line, we analytically show that in the magnetically-dominated relativistic regime, the x-line thermal pressure is significantly lower than the upstream magnetic pressure due to the extreme energy needed to sustain the current density, consistent with kinetic simulations. This causes the upstream magnetic field lines to collapse in, producing the open outflow geometry which enables fast reconnection. The result is important for understanding a wide range of extreme astrophysical environments, where fast reconnection has been evoked to explain observations such as transient flares and nonthermal particle signatures.