Aspects of turbulence in protostellar accretion discs are being reviewed. The emergence of dead zones due to poor ionization and alternatives to the magneto-rotational instability are discussed. The coupling between dust and gas in protostellar accretion discs is explained and the turbulent drag is compared with laminar drag in the Stokes and Epstein regimes. Finally, the significance of magnet...

1. The two main models for planet formation in discs are ‘core accretion’ and ‘gravitational instability’ 2. Gravitational instability requires massive discs that satisfy the Toomre criterion and a sufficiently fast cooling rate 3. Core accretion proceeds in stages from dust to planetesimals, to terrestrial planets and eventually gas giants. Several ‘growth barriers’ must be overcome. 4. Both m...

I solve analytically the viscous evolution of a self–irradiated accretion disc, as seen during outbursts of soft X–ray transients. The solutions predict steep power–law X– ray decays LX ∼ (1 + t/tvisc) , changing to LX ∼ (1 − t/t ′ visc ) at late times, where tvisc, t ′ visc are viscous timescales. These forms closely resemble the approximate exponential and linear decays inferred by King and R...

Steady state accretion discs larger than ∼ 0.01−0.1 pc are known to be gravitationally unstable for the accretion rates needed to explain super-massive black hole (SMBH) activity. We propose that SMBH are fed by a succession of mass deposition events with randomly directed angular momenta. Because of incomplete angular momentum cancellation a warped accretion disc forms in the inner few parsec....

An accretion disc around a compact star in a close binary star system is an ubiquitous and essential object. Accretion discs play, for example, important roles in cataclysmic variables, nova and X-ray sources. The standard theory to explain the physics in accretion discs is the α-disc model proposed by Shakura and Sunyaev (1973). In this theory, the accretion disc is in some kind of turbulent s...