 Astrophysical fluid dynamics

Astrophysical fluid dynamics models gases and plasmas in stars, accretion discs, stellar winds and other astronomical flows. Its distinctive ingredients can include self-gravity, rotation, compressibility, radiative cooling and magnetic fields. ^[ref]

A useful scale comparison is the Mach number $\mathrm{Ma}=U/c_s$, with flow speed $U$ and sound speed $c_s$. Large compressions can produce shock waves; self-gravity can instead amplify density disturbances through Jeans instability. Conducting plasma adds magnetohydrodynamics. A continuum approximation must be justified: a very tenuous medium can require a kinetic description instead of a simple collisional fluid.