Abstract: Stars form from the gravitational collapse and fragmentations of turbulent clouds which mostly lead to the birth of dense but short-lived, transient clusters. Collapse is opposed by the "Feedback Ladder" of ever more powerful feedback mechanisms as stars gain mass. Most forming stars drive jets and bipolar outflows while they accrete. Massive stars ionize their environments, drive stellar winds, and eventually explode as supernovae. These processes disrupt the natal clouds. The nearest massive star forming region, Orion, was the site of a ~10^48 erg protostellar explosion about 550 years ago (that is when the signal reached Earth). Debris is still expanding through the gas immediately behind the Orion Nebula. The explosion was associated with the ejection of three runaway stars, one of which is likely a merger remnant. This event was triggered by the N-body interaction of at least 4 stars. Among massive stars, protostellar explosions occur at least once a century in the Milky Way, comparable to the Galactic supernova rate. Dynamical ejections also occur in low-mass star forming regions; N-body interactions, combined with feedback, may determine final stellar masses. I will discuss the implications of these results for the formation of massive stars and the IMF. The talk will be illustrated with lots of observations.
