Local Radiation Hydrodynamic Simulations of Massive Star Envelopes at the Iron Opacity Peak

Understand

We perform three dimensional radiation hydrodynamic simulations of the structure and dynamics of radiation dominated envelopes of massive stars at the location of the iron opacity peak.

• One dimensional hydrostatic calculations predict an unstable density inversion at this location, whereas our simulations reveal a complex interplay of convective and radiative transport whose behavior depends on the ratio of the photon diffusion time to the dynamical time.
• The latter is set by the ratio of the optical depth per pressure scale height, $\tau_0$, to $\tau_c=c/c_g$, where $c_g \approx$ 50 km/s is the isothermal sound speed in the gas alone.
• When $\tau_0 \gg \tau_c$, convection reduces the radiation acceleration and removes the density inversion.