Star Formation in the Early Universe: what drove the transition from Population III to Population II?

Greg Bryan (Columbia)

Theoretical and observational evidence indicates that the first generation of stars to form in the universe were typically quite massive, and consequently lived short lives. However, low mass stars with extremely low metallicity exist in the halo of the Milky Way, indicating that star formation transitioned to a mode that allowed low mass stars to form. This is typically explained by the enhanced cooling arising from the heavy elements ejected in the first supernovae, but the full story may be much more involved, with cooling playing only a supporting role. In this talk, I will discuss the theoretical ideas behind the transition from high mass to low-mass star formation as well as the observational constraints from current and future surveys of local stars.