Apr 06, 2017
Fausto Cattaneo, University of Chicago
""Turbulence and Dynamo Action in Accretion Flows""
Accretion is an important process in astrophysics: it allows the growth of compact objects and it powers some of the most energetic phenomena in the universe. Often the accreting material comes from a disk. In this case the accretion rate is controlled by the outward flux of angular momentum. Collisional process, like viscosity, are many orders of magnitude too small to provide the efficient angular momentum transport required to account for the observed accretion rates. Thus it is commonly assumed that the transport in an accretion disk is mediated by some form of turbulence. The nature of this turbulence is a matter of intense debate. In electrically conducting disks, its origin is most likely related to the Magneto Rotational Instability (MRI), which requires that the disk be threaded by a coherent weak magnetic field. This raises the interesting possibility that the disk turbulence, through dynamo action, may be able to generate the very magnetic filed that is necessary for the instability to develop. This process of self-sustaining magnetization has indeed been observed in numerical simulations. However many issues remain, the most notable of which are the ability of the MRI driven dynamo to operate in the limit of high electrical conductivity and the efficiency of the angular momentum transport. In this talk I shall describe some of the efforts to date to address these issues.