(updated for 2013)
- Galactic rotation: 18 km/s/kpc (e.g. 180 km/s at 10 kpc)
- Isothermal sound speed:
- For H, this speed is 0.3, 1, and 3 km/s at 10 K, 100 K, and 1000 K, respectively.
- Alfvén speed: The speed at which magnetic fluctuations propagate. Alfvén waves are transverse waves along the direction of the magnetic field.
- Note that if , which is observed to be true over a large portion of the ISM.
- Interstellar B-fields can be measured using the Zeeman effect. Observed values range from in the diffuse ISM to in dense clouds. For specific conditions:
- Compare to the isothermal sound speed, which is 0.3 km/s in dense gas at 20 K.
- in dense gas
- in diffuse gas
- Observed velocity dispersion in molecular gas is typically about 1 km/s, and is thus supersonic. This is a signature of the presence of turbulence. (see the summary of Larson’s seminal 1981 paper)