The Formation of Massive Stars by Accretion through Trapped Hypercompact H II Regions

The formation of massive stars may take place at relatively low accretion rates over a long period of time if the accretion can continue past the onset of core hydrogen ignition. The accretion may continue despite the formation of an ionized H II region around the star if the H II region is small enough that the gravitational attraction of the star dominates the thermal pressure of the H II region. The accretion may continue despite radiation pressure acting against dust grains in the molecular gas if the momentum of the accretion flow is sufficient to push the dust grains through a narrow zone of high dust opacity at the ionization boundary and into the H II region where the dust is sublimated. This model of massive star formation by continuing accretion predicts a new class of gravitationally trapped, long-lived, hypercompact H II regions. The observational characteristics of the trapped hypercompact H II regions can be predicted for comparison with observations.