The role of reconnection diffusion in the gravitational collapse of turbulent cloud cores

Abstract

For a molecular cloud clump to form stars some\ud transport of magnetic flux is required from the\ud denser, inner regions to the outer regions of the\ud cloud, otherwise this can prevent the collapse. Fast\ud magnetic reconnection which takes place in the presence\ud of turbulence can induce a process of reconnection\ud diffusion (RD). Extending earlier numerical\ud studies of reconnection diffusion in cylindrical\ud clouds, we consider more realistic clouds with spherical\ud gravitational potentials and also account for the\ud effects of the gas self-gravity. We demonstrate that\ud within our setup RD is efficient. We have also identified\ud the conditions under which RD becomes strong\ud enough to make an initially subcritical cloud clump\ud supercritical and induce its collapse. Our results indicate\ud that the formation of a supercritical core is\ud regulated by a complex interplay between gravity,\ud self-gravity, the magnetic field strength and nearly\ud transonic and trans-Alfv´enic turbulence, confirming\ud that RD is able to remove magnetic flux from collapsing\ud clumps, but only a few of them become nearly\ud critical or supercritical, sub-Alfv´enic cores, which is\ud consistent with the observations. Besides, we have\ud found that the supercritical cores built up in our simulations\ud develop a predominantly helical magnetic\ud field geometry which is also consistent with observations.\ud Finally, we have evaluated the effective values\ud of the turbulent reconnection diffusion coefficient and found that they are much larger than the numerical\ud diffusion, especially for initially trans-Alfv´enic\ud clouds, ensuring that the detected magnetic flux removal\ud is due to to the action of the RD rather than\ud to numerical diffusivity.Resumo publicado no periódico: Revista Mexicana de Astronomía y Astrofísica. Serie de Conferencias, v. 44, p. 140-141, 2013