94230 - Astrophysical Fluid Dynamics

Learning outcomes

The aim of the course is to provide the student with the main theoretical tools to study the dynamics of fluids in astrophysical systems such as stars, accretion discs, galaxies and clusters of galaxies. At the end of the course the student will be familiar with the analytic modelling of hydrodynamic-equilibrium configurations of fluids in gravitational potentials, of gas flows and of hydrodynamic instabilities. In addition the student will have some knowledge of the role of magnetic fields in the dynamics of astrophysical fluids.

Course contents

- Fundamentals of astrophysical fluid dynamics: mass, momentum and energy conservation, equation of state, gravity, cooling, heating,
thermal conduction, viscosity and turbulence .

- Equilibrium of astrophysical fluids: self-gravity and external
gravitational potentials, hydrostatic equilibrium (isothermal,
adiabatic and polytropic distributions), virial temperature, isothermal self-gravitating plane layer, self-gravitating isothermal gas sphere, rotating equilibrium (barotropic and baroclinic distributions), thin and thick discs.

- Hydrodynamic stability and instability: Eulerian and Lagrangian
perturbations, linear and non-linear perturbations, sound waves,
gravitational (Jeans) instability, convective (Schwarzschild)
instability, rotation (Rayleigh) instability, Solberg-Hoiland
criterion, thermal instability, Toomre instability.

- Gas flows in galaxies: steady inflows and outflows, shocks, gas
accretion onto black holes (Bondi accretion, Eddington limit).

- Astrophysical magnetohydrodynamics (MHD): MHD equations,
equilibrium of magnetised gas, Ferraro's law of isorotation, magnetosonic and Alfvén waves, magnetorotational instability.

Readings/Bibliography

- M. J. Thompson "An introduction to astrophysical fluid dynamics", 2006, Imperial College Press

- J. Pringle and A. King "Astrophysical flows", 2014, Cambridge University Press

- C. Clarke and B. Carswell "Principles of Astrophysical Fluid Dynamics", 2014, Cambridge University Press

- A. Cimatti, F. Fraternali and C. Nipoti, "Introduction to Galaxy Formation and Evolution. From Primordial Gas to Present-Day Galaxies", 2019, Cambridge University Press

- F. Shu "The physics of astrophysics", 1992, University Science Books

- Binney, J., and Tremaine, S. 2008. Galactic Dynamics: Second Edition. Princeton University Press.

- Landau, L. D., and Lifshitz, E. M. 1959. Fluid mechanics

Specific sections of textbooks and articles will be suggested during the lectures. Lecture notes will be made available to the students.

Teaching methods

Lectures

Assessment methods

The assessment method will be based on an oral exam in which the
student will be asked to answer three questions about three different
topics among those presented during the lectures. The oral exam
is aimed at verifying the knowledge of the theory of fluid dynamics phenomena and the understanding of the main astrophysical applications.

Teaching tools

Blackboard and projector

Office hours

See the website of Carlo Nipoti