Tuesday, September 11, 2012

1209.1846 (M. R. M. Leão et al.)

Cloud core collapse and the role of turbulent magnetic reconnection diffusion    [PDF]

M. R. M. Leão, E. M. de Gouveia Dal Pino, R. Santos-Lima, A. Lazarian
For a molecular cloud clump to form stars some transport of magnetic flux is required from the denser, inner regions to the outer regions of the cloud, otherwise this can prevent the gravitational collapse. Fast magnetic reconnection which takes place in the presence of turbulence can induce a process of reconnection diffusion. This paper continues our numerical study of this process and its implications. In particular, extending our earlier studies of reconnection diffusion in cylindrical clouds we consider more realistic clouds with spherical gravitational potentials (from embedded stars) and also account for the effects of the gas self-gravity. We demonstrate that within our setup reconnection diffusion takes place. We have also derived the conditions under which reconnection diffusion becomes efficient enough to make an initially subcritical cloud clump to become supercritical and collapse. Our results indicate that the formation of a supercritical core is regulated by a complex interplay between gravity, self-gravity, the magnetic field strength and nearly transonic and trans-Alfv\'enic turbulence. In particular, self-gravity helps reconnection diffusion and, as a result, the magnetic field decoupling from the collapsing gas gets more efficient compared to the case of an external gravitational field. We demonstrate that reconnection diffusion is able to remove magnetic flux from collapsing clumps, but only a few of them develop nearly critical or supercritical cores, which is consistent with the observations. Their formation is restricted to a range of initial conditions for the clouds.
View original: http://arxiv.org/abs/1209.1846

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