Continuum-driven versus line-driven mass loss and the Eddington limit

Basic stellar structure dictates that stars of ∼ 100 M_⊙ or more will be close to the Eddington limit, with luminosities in excess of 10⁶ L_⊙, and radiation pressure contributing prominently to the support against gravity. Although it is formally possible to generate static structure models of even more massive stars, recent studies of dense clusters show there is a sharp cutoff at masses above ∼ 150 M_⊙. This talk examines the role of extreme mass loss is limiting the masses of stars, emphasizing in particular that continuum driving, possibly associated with structural instabilities of radiation dominated envelope, can lead to much stronger mass loss than is possible by the usual line-scattering mechanism of steady stellar winds.