Please note: the animated gif file is large (9 MB) and it may take a while to load it into cache. Once there, however, the movie plays at its intended speed. So, please be patient.

Simulation of a line driven wind from an accretion disk

• The wind is driven by radiation pressure in spectral lines
• The gas in the (massless) disk accretes onto a dark central star
• Such a wind could occur in Cataclysmic Variables or in Young Stellar Objects (or, with certain alterations, in AGN)
• The disk extends from 1 to 30 stellar radii along the x-axis
• The disk gas is on Keplerian orbits
• The temperature run in the disk as function of radius is T ~ r^(-1/2)
• The overall disk Eddington factor is 0.01 for Thomson scattering on electrons
• ...which implies an Eddington factor of ~ 20 for scattering in spectral lines!
• The wind is driven by momentum transfer (and not primarily by energy transfer) from disk photons to metal ions
• Coulomb collisions distribute this momentum gain over the whole plasma (mostly ionized hydrogen)
• The movie shows the density above the disk, where thin regions are in white, dense regions are in black
• The movie starts from a rather arbitrary initial model
• ...but the final images show a quasi-periodic limit cycle of dense streamers above the disk

If you want to read three papers on hydrodynamics of line driven winds, my recommendations are

1. Castor, Abbott, and Klein, 1975, Radiation-driven winds in Of stars , Astrophysical Journal, 195, 157
   (Tough reading, but it's all there)

2. Owocki and Rybicki, 1986, Instabilities in line-driven stellar winds. III. Wave propagation in the case of pure line absorption , Astrophysical Journal, 309, 127
   (For the mathematical surprises encountered for wave propagation in unstable media)

3. Blondin, Kallman, Fryxell, and Taam, 1990, Hydrodynamic simulations of stellar wind disruption by a compact X-ray source , Astrophysical Journal, 356, 591
   (For what are probably still the most impressive images from a 2-D wind simulation)