Astrophysical Implications of Turbulent Reconnection: from cosmic rays to star formation

Turbulent reconnection allows fast magnetic reconnection of astrophysical magnetic fields. This entails numerous astrophysical implications and opens new ways to approach long standing problems. I briefly discuss a model of turbulent reconnection within which the stochasticity of 3D magnetic field enables rapid reconnection through both allowing multiple reconnection events to take place simultaneously and by restricting the extension of current sheets. In fully ionized gas the model in Lazarian & Vishniac 99 predicts reconnection rates that depend only on the intensity of turbulence. In partially ionized gas a modification of the original model in Lazarian, Vishniac & Cho 04 predicts the reconnection rates that, apart from the turbulence intensity depend on the degree of ionization. In both cases the reconnection may be slow and fast depending on the level of turbulence in the system. As the result, the reconnection gets bursty, which provides a possible explanation to Solar flares and possibly to gamma ray busts. The implications of the turbulent reconnection model have not been yet studied in sufficient detail. I discuss first order Fermi acceleration of cosmic ray that takes place as the oppositely directed magnetic fluxes move together. This acceleration would work in conjunction with the second order Fermi acceleration that is caused by turbulence in the reconnection region. In partially ionized gas the stochastic reconnection enables fast removal of magnetic flux from star forming molecular clouds. WHAT IS MAGNETIC RECONNECTION? Magnetic fields play key role for many Astrophysical processes like star formation, cosmic ray transport and acceleration, accretion etc. As a rule, magnetic diffusivity is slow over huge astrophysical scales and therefore frozenness of magnetic field provides an excellent approximation (see Moffatt 1978). Magnetic field lines in astrophysical highly conducting fluids act as elastic threads that are moved together with the fluid. However, fluid motions are likely to create knots in which magnetic threads will be pressing against each other. If the state of frozenness is not violated at these knots this would result in the formation of felt or Jello-like structure of magnetic field that is favored by some astrophysicists (Cox 2004). If, however, crossing magnetic field lines can change their topology, the dynamics of magnetized fluid is completely different. The situation is rather dramatic. In fact, we cannot claim that we understand the dynamics of magnetized astrophysical fluids if we cannot figure out what picture is correct, i.e. whether astrophysical fluids act as a magnetic Jello or have fluid type behavior (see more below). Note, that adopting the first alternative would also mean kiss of death to the contemporary dynamo theories, i.e. to the theories that explain magnetism