COLLAPSE OF MOLECULAR CLOUD CORES WITH RADIATION TRANSFER: FORMATION OF MASSIVE STARS BY ACCRETION

Most early radiative transfer calculations of protostellar collapse have suggested an upper limit of ∼40 Msun for the final stellar mass before radiation pressure can exceed the star's gravitational pull and halt the accretion. Here we perform further collapse calculations, using frequency-dependent radiation transfer coupled to a frequency-dependent dust model that includes amorphous carbon particles, silicates, and ice-coated silicates. The models start from pressure-bounded, logatropic spheres of mass between 5 Msun and 150 Msun with an initial nonsingular density profile. We find that in a logatrope the infall is never reversed by the radiative forces on the dust and that stars with masses ∼>100 Msun may form by continued accretion. Compared to previous models that start the collapse with a ρ ∝ r-2 density configuration, our calculations result in higher accretion times and lower average accretion rates with peak values of ∼5.8 x 10-5 Msun yr-1. The radii and bolometric luminosities of the produced massive stars (∼>90 Msun) are in good agreement with the figures reported for detected stars with initial masses in excess of 100 Msun. The spectral energy distribution from the stellar photosphere reproduces the observed fluxes for hot molecular cores with peaks of emission from mid- to near-infrared.