Institute for Advanced Study Astrophysics Seminar

With the progress of collisionless Hall-MHD reconnection models a really burning question arises. Is the reconnection rate fast in collisionless environments and slow when collisions are important? The positive answer to that question means that all MHD simulations, including those of interstellar medium, do not represent astrophysical reality, as high diffusivity of codes makes numerical reconnection fast. I shall discuss the results new 3D MHD numerical simulations that support the model of reconnection proposed in Lazarian & Vishniac (1999). This model does not appeal to any plasma physics effects and provides fast reconnection of magnetic field in the presence of weak magnetic field stochasticity. The simulations provided in a generic 3D configuration with a substantial guide field provide reconnection rates which do not depend on the Ohmic resistivity, but are functions of the turbulence injection strength and the turbulence injection scale. The observed dependences correspond to the theoretical predictions. The model is applicable to both collisionless and collisional environments and does not show dependences on anomalous resistivities that were introduced in some of the numerical runs to mimic plasma effects. The predictions of the model include First Order Fermi acceleration of energetic particles, flares of reconnection, which can be associated with Solar Flares etc.