Radiation Pressure in Massive Star Formation

Context: During their evolution, massive stars quickly become so luminous that their radiation pressure onto the environment exceeds their gravitational attraction. Hence, radiation pressure plays a major role in shaping the circumstellar environment. Methods: Numerical highlights of our 1D, 2D, and 3D self-gravity radiation hydrodynamics simulations of various collapsing pre-stellar cores of gas and dust include a grid in spherical coordinates with non-uniform resolution down to 1 AU (Kuiper et al. 2010, ApJ 722), a highly accurate frequency-dependent ray-tracing approach of the stellar irradiation (Kuiper et al. 2010, A&A 511), and the consideration of temperature- and density-dependent gas opacities (Kuiper & Yorke 2013, ApJ). Results: We determine the impact of the radiation pressure on the forming accretion disk and the bipolar outflow cavities: a) The well-known radiation pressure problem in the formation of massive stars can be circumvented via classical disk accretion: The formation of long-living massive accretion disks enforces a strong anisotropy of the thermal radiation field, enabling steady accretion through the shielded disk region (Kuiper et al. 2010, ApJ 722). b) This so-called flashlight effect is even amplified by optically thick gas (disks) around forming massive protostars (Kuiper & Yorke 2013, ApJ). c) In 3D the self-gravity of the massive accretion disk drives a sufficiently high angular momentum transport enabling the accretion flow to overcome the residual radiation pressure (Kuiper et al. 2011, ApJ 732). d) Treating the stellar irradiation in the gray FLD approximation underestimates the radiative forces acting on the cavity shell. This can artificially lead to situations unstable to the radiative Rayleigh-Taylor instability (Kuiper et al. (2012), A&A 537). Conclusions: Summing up, the various simulation series draw a consistent picture of the formation of even the most massive (> 100 Msol) stars by classical disk accretion.