Accretion Processes in Astrophysics ASTM003 Lecturer: Dr. Richard Nelson Office: 453 Extn: 5199 Email: R.P.Nelson@qmul.ac.uk Lecture Times: 6:30 - 9:00pm, Friday evenings, 16/01/04 - 20/02/04 Lecture Room: M103 Aims and Objectives: This course aims to provide students with a knowledge of the theory and phenomenology of accretion discs in astrophysics. The important physical processes associated with accretion discs are described, and their application to protostellar discs, close binary systems containing a compact object (white dwarf, neutron star, or black hole), and planet formation are explored. The key objectives of the course are to provide students with knowledge and understanding of: Protostellar disc formation Discs in close binary systems Angular momentum transfer mechanisms that drive accretion disc evolution Theory of viscous disc evolution and derivation of the `diffusion equation' Interaction of discs with stellar magnetospheres Planet formation and disc-planet interactions Books: There are no books that provide complete coverage for this course. However the most comprehensive textbook on accretion discs is `Accretion Power in Astrophysics' by Juhan Frank, Andrew King, and Derek Raine, published by Cambridge University Press. The lectures will be organised as follows: Lecture 1: Introduction to the role of angular momentum in astrophysics. Phenomenological description of astronomical objects in which differentially rotating systems are found (accretion discs, planetary rings, galactic discs, planetary systems). Rotation laws and balance between centrifugal and gravitational forces. Equations of motion for self-gravitating, magnetised, inviscid fluid will be introduced. The virial theorem for rotating, magnetised fluid masses. Lecture 2: Protostellar disc formation via cloud collapse, including criteria for collapse of molecular clouds, and estimates of disc sizes. Comparison with observations. Disc formation in close binary systems. The Roche potential. Classification of semi-detached binary systems in which discs form (cataclysmic variables, low-mass X-ray binaries, X-ray binaries). Close binary formation scenarios, and Roche lobe overflow. Disc sizes and requirement for compact objects. Observations of C.V. discs and dwarf novae outbursts. Lecture 3: Accretion onto compact objects as powerful energy sources. Angular momentum transfer mechanisms in differentially rotating discs. Viscosity, global magnetic fields and disc winds, wave transport through tidal interaction. Vertical structure and hydrostatic equilibrium. Derivation of diffusion equation for surface density evolution. Time scales for viscous evolution, and requirement of anomalous viscosity in discs. Lecture 4: Steady state disc theory. Energy production in discs and viscous dissipation as energy source. Temperature profiles in steady state discs. Application to protostars, C.V.s, X-ray binaries, and active galactic nuclei. Eddington limited accretion. Lecture 5: Spectrum of optically thick discs and derivation of power law relation between luminosity and frequency. The boundary layer as source of additional energy. Disc-stellar magnetosphere interaction - derivation of expressions for torques acting on disc due to stellar magnetic field. Disc truncation due to magnetospheric interaction. Apply to T Tauri star rotation rates, spin-up/spin-down of pulsars. Lecture 6: Protostellar discs and planet formation. Properties of discs around T Tauri stars. Minimum mass solar nebula models. Estimates of grain growth time scales, and time scales for planetesimal growth. Formation of terrestrial planets. Formation of giant planets. Disc-protoplanet tidal interactions, gap formation, and orbital migration. Application to extrasolar planets.