We examine the conditions imposed on the vertical structure of accretion discs for them to exist. We find that a wind powered by a thermal instability exists in all discs with certain opacity laws. We find that for discs dominated by bremsstrahlung radiation, an inner hole develops below a certain accretion rate, and that for very low accretion rates, discs may not form at all. The consequences...

magnetic fields play an important role in creating, driving, and in the evolution of outflows and jets from protostars and accretion disks. on the other hand, the temperature profile of the accretion disks may also affect the structure of the magnetic field and outflows. in this paper, we use the self-similar method in cylindrical coordinates to investigate the effect of the temperature profile...

We show that radiation dominated accretion discs are likely to suffer from a “photon bubble” instability similar to that described by Arons in the context of accretion onto neutron star polar caps. The instability requires a magnetic field for its existence. In an asymptotic regime appropriate to accretion discs, we find that the overstable modes obey the remarkably simple dispersion relation

Using a local model Gammie (2001) has shown that accretion discs with cooling times tcool ≤ 3Ω −1 fragment into gravitationally bound objects, while those with cooling times tcool > 3Ω −1 evolve into a quasi-steady state. We use three-dimensional smoothed particle hydrodynamic simulations of protoplanetary accretion discs to test if the local results hold globally. We find that for disc masses ...

Some recent results are reviewed that lead us now to believe that accretion discs are basically always magnetised. The main components are Balbus-Hawley and Parker instabilities on the one hand and a dynamo process on the other. A mechanical model for the Balbus-Hawley instability is presented and analysed quantitatively. Three-dimensional simulations are discussed, especially the resulting mag...

— I review recent progresses in the dynamics and the evolution of self-gravitating accretion discs. Accretion discs are a fundamental component of several astrophysical systems on very diverse scales, and can be found around supermassive black holes in Active Galactic Nuclei (AGN), and also in our Galaxy around stellar mass compact objects and around young stars. Notwithstanding the specific di...