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

Abstract

Most early radiative transfer calculations of protostellar collapse have suggested an upper limit of ∼40 M☉ 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 M☉ and 150 M☉ 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 M☉ 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 × 10−5M☉ yr−1. The radii and bolometric luminosities of the produced massive stars (≳90 M☉) are in good agreement with the figures reported for detected stars with initial masses in excess of 100 M☉. 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.