Once upon a time, we astrophysicists told nice stories about giant gravitationally-bound blobs of gas, which we called “Giant Molecular Clouds," in the Galaxy that broke up somehow into smaller, gravitationally-bound, blobs that ultimately collapsed under their own weight to make stars.  We called the smallest of those blobs “Dense Cores.” Along the way there was some messiness, involving gas that missed becoming part of the star squirting outward in outflows and jets, and, also, there were some little leftovers that today we call planets.  

 

Today, some people still tell this story, but it seems, in the light of ever-clearer and higher-resolution observations and simulations of the star formation process, large passages of the old-timey story are untrue, or at best misleading. Instead, star-formation seems a bit more like urban population growth.  Cities form for only somewhat predictable reasons.  They “accrete” or “expel” inhabitants based on properties that are only sometimes easy to understand.   Maybe there are good roads to a city?—or maybe many other people have already decided that a particular city is a great place to live?  Once a city is established, it gets crowded and complicated, and it begins to shed disgruntled inhabitants in violent uprisings, potentially driving away potential new immigrants.  

 

There are, of course, physics-based explanations for these apparent demographic trends, and this talk will look at recent observations across the electromagnetic spectrum alongside recent simulations, to ponder whether or not a “demographic” approach to understanding the star-formation process within  “unbound” gas makes sense.