Speaker: Tab Tanvir, Iowa State University

Host: Jake Simon

Title: When Did the Universe Learn to Make Low-Mass Stars?

Abstract: The stellar initial mass function (IMF) is one of the fundamental outcomes of star formation, shaping stellar feedback, chemical enrichment, and galaxy evolution. Its low-mass turnover is particularly important because it marks the emergence of a characteristic stellar mass scale. In nearby, Milky Way-like environments, this scale appears remarkably stable, yet observations of more extreme systems suggest that the IMF may vary, raising a basic theoretical question: what physical conditions set the turnover, and how universal should it really be? Theoretical models increasingly point toward an environmental origin for this mass scale. Controlled calculations show that increasing cloud surface density produces lower characteristic masses and narrower stellar mass distributions through the combined effects of fragmentation, radiative heating, and protostellar outflows. By comparison, variations in metallicity produce much smaller changes in the IMF at fixed surface density, despite substantially altering the thermal state of the gas. These results suggest that no single environmental variable controls the IMF turnover; instead, it emerges from the interaction between thermodynamics, cloud structure, feedback, and dynamics. This naturally extends the problem to the earliest epochs of star formation: when did the physical conditions required for a low-mass stellar population first arise? Understanding how the characteristic stellar mass changes from primordial star formation to present-day environments provides a way to connect the physics of the IMF across cosmic history.