Abstract:
Accretion disks are a basic and an ubiquitous construct of nature. We describe their formation, briefly and qualitatively, in diverse astrophysical situations. These systems, though controlled by the gravitational forces, have embedded in them a host of magnetohydrodynamic (MHD) and plasma-physical mechanisms without which many an observed phenomena would be hard to account for. The essential role of the MHD turbulence has been well emphasized. We give, here, a critical review of the ways and means of generating it through the magnetorotational instability and in the process correct the erroneous premise on which the local analysis continues to be carried out. The problem is complex and the present level of its understanding leaves much that needs novel techniques to fully capture its entire range of processes.
