The course will be concerned mainly with the fluid dynamics of stars and their interactions with the surrounding interstellar medium. It begins with a brief derivation of the equations governing the motion of compressible fluids, from which some basic properties of fluid flow can immediately be derived.
Stars form as a result of gravitational instability of large gas clouds.
The details of the nonlinear development of the instability are not understood, but in the final stages a star has formed and matter is accreting onto it in a radiating disc of circulating material. The matter is essentially in Keplerian orbits, but there is a slow transfer of angular momentum by turbulent viscous drag, dissipating the rotational kinetic energy and the gravitational energy and causing the disc to shine in a characteristic manner. The winds impinge upon the interstellar material, causing shocks to develop, and to heat and ionize the gas, the energy from which is subsequently radiated by a variety of processes. The internal structure of stars can be understood extremely well if it is assumed that they are spherically symmetrical and, except in well defined convections zones, hydrodynamically quiescent for most of their existence. In the convection zones, the effects of motion can be analysed by considering mean energy and momentum transport.