69055 - Gas Dynamics in Galaxies

Course Unit Page

Academic Year 2016/2017

Learning outcomes

The student will get acquainted with the theory of ideal and viscous gases and its application to the study of the interstellar medium in galaxies. In particular, they will be able to describe the processes of star formation and stellar feedback. They will also acquire a broad knowledge of the main observational techniques (e.g. of optical and radio emission lines) that allow the study of gas kinematics in galaxies.

Course contents

1. Overview on ISM: Composition and spatial distribution in galaxies, phases and equilibria, cooling and heating, Maxwellian distribution.
2. Ideal gas dynamics: Equation of continuity and Euler eq.; Pressure; Equation of state: Barotropic, adiabatic and isothermal flows; Energy equation; Heat sources: conduction and radiation; Entropy and the heat equation; Propagation of sound waves, sound speed; Hydrostatics: isothermal slab, z-distribution with stars; Shock waves and instabilities: Jump conditions; Adiabatic shocks; Entropy jump in adiabatic shocks; Radiative shocks; Convection; Instabilities: Rayleigh-Taylor, Kelvin-Helmholtz, Gravitational, Rotational, and Thermal.
3. Viscous fluids and turbulence: Momentum flux and stress tensor; Viscous stress tensor; Navier-Stokes equation; Vorticity in ideal and viscous fluids; Energy dissipation in viscous flows; General heat equation; Reynolds number; Transition to turbulence in a Poiseuille flow; Fully developed turbulence, Kolmogorov law; Compressible turbulence, sources of turbulence in the ISM.
4. Molecular clouds: composition and properties. Plasmas: Charge neutrality, infinite conductivity; Field freezing; Euler equation with magnetic force; Magnetic Pressure and tension; Magnetic virial theorem; Shocks with magnetic field. Stability of clouds: Isothermal sphere, Lane-Emden equation; Bonnor-Ebert sphere and mass; Analysis of stability; Effect of rotation; Effect of magnetic field; Hydromagnetic waves; The role of turbulence. Collapse of clouds: Free-fall time; Self-similar collapse; Ambipolar diffusion, magnetic braking.
5. Effect of massive stars on the ISM (feedback): Evolution of SNRs - adiabatic phase; Sedov -Taylor solutions for shell interior; Pressure driven and Snowplow phases; Energy budget; Stellar wind bubbles: structure and self similar solution; Temperature, pressure & evolutionary phases; Energy budget; Superbubbles: evolution, blowout, SNR inside superbubbles; Galactic fountain and winds.


Principles of Astrophysical Fluid Dynamics, C. J. Clarke & R. F. Carswell, Cambridge University Press   

The Physics of Astrophysics II: Gas dynamics, F. H. Shu, University Science Books

The Formation of Stars, S. W. Stahler & F. Palla, Wiley-VCH

Physical Processes in the Interstellar Medium, L. Spitzer, Wiley-VCH

Teaching methods

Lectures can be in ENGLISH if there are non-italian speaking students

Assessment methods

Oral exam

Teaching tools

Blackboard and powerpoint presentations.

Links to further information


Office hours

See the website of Filippo Fraternali