Development of a turbulent outflow during electron-positron magnetic reconnection

The mass symmetry between the two species in electron-positron (pair) plasmas has interesting consequences for collisionless magnetic reconnection, because the Hall term, which plays a crucial role in supporting fast reconnection in electron-proton plasmas, vanishes. We perform kinetic simulations of pair reconnection in systems of various sizes, show that it remains fast, and identify the reason why this occurs. For sufficiently large systems a Weibel-like temperature anisotropy instability develops in the outflow from the X-point that causes the current layer to broaden and form a Petschek-like open outflow. We discuss the parameter regimes in which pair reconnection should be fast and the implications for astrophysical pair plasmas.