interstellar medium. These effects strengthen after their short main sequence lifetime, through the supergiant and Wolf-Rayet phases, and culminates in the most energetic of stellar events, the supernova explosion. Thus, the energy input from massive stars, via the combined effects of expanding H II regions and supernova remnants, can shape the interstellar medium of gaseous galaxies, creating large, expanding structures that may even vent mass and energy into the halo. It is this litany of energetic phenomena that gives massive stars such a pivotal role in astrophysics. Hence, it is not surprising to find that the dynamics of these phenomena have figured strongly in John’s work over the years.

Accretion
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Larson & Starrfield (1971) and John’s mentor, Kahn (1974), first investigated one of the intriguing questions in massive star formation - how can accretion continue in the face of extreme radiation pressure. This results from another key difference between low and high mass star formation. The timescale for contraction in to a main sequence configuration is shorter than the formation timescale for massive stars. Hence, they are probably still accreting at the surface when hydrogen burning begins in the core. As the mass increases the luminosity from fusion and 