We investigate the apparent discrepancy between gas and dust outer radii derived from millimeter observations of protoplanetary disks. Using 230 and 345 GHz continuum and CO J=3-2 data from the Submillimeter Array for four nearby disk systems (HD 163296, TW Hydrae, GM Aurigae, and MWC 480), we examine models of circumstellar disk structure and the effects of their treatment of the outer disk ed...

The origin of hydrodynamic turbulence, and in particular of an anomalously enhanced angular momentum transport, in accretion disks is still an unsolved problem. This is especially important for cold disk systems which are practically neutral in charge and therefore turbulence can not be of magnetohydrodynamic origin. While the flow must exhibit some instability and then turbulence in support of...

We consider the combined role of the thermal ionization, magneto-rotational and gravitational instabilities in thin accretion disks around supermassive black holes. We find that in the portions of the disk unstable to the ionization instability, the gas remains well coupled to the magnetic field even on the cold, neutral branch of the thermal limit cycle. This suggests that the ionization insta...

Twenty five years have passed by since models of accretions and jets have separately emerged. Today, it is understood that these two objects are related to each other in a fundamental way. In a binary system, matter from an accretion disk enters into a black hole. A part of it is bounced back because of the centrifugal barrier, radiation pressure or magnetohydrodynamic effects, to form jets and...