Theories of Massive Star Formation: Collisions, Accretion and the View   from the "I" of Orion
  I review the arguments motivating models for massive star formation via stellar collisions. I then describe how the standard accretion scenario, involving the collapse of a quasi-hydrostatic gas core, can produce high-mass stars in the pressurized regions of forming star clusters. I argue that the observational evidence, particularly in the Orion hot core, favors the standard accretion paradigm. 
Jonathan C. Tan (Princeton University Observatory)