Depicting the Early Evolution of Globular Clusters Through the Lens of Multiple Stellar Populations

Abstract

A major paradigm shift has recently revolutionized the classical picture depicting globular star clusters (GC) as simple systems of coeval stars born out of homogeneous material. Indeed, detailed spectroscopic studies of GC long-lived low-mass stars performed with 8–10 m class telescopes, together with high-precision photometry of Galactic GCs obtained with HST, have brought compelling evidences on the presence of multiple stellar populations in individual GCs. These stellar subgroups can be recognized thanks to their different chemical properties (more precisely by abundance differences of light elements from carbon to aluminium) and in some cases by the appearance of multimodal sequences in the GC colour-magnitude diagrams. These findings have opened unexpected roads to do GC archeology. They provide in particular invaluable clues on the possible ways massive stars have shaped the intra-cluster medium evolution (ICM) and induced secondary star formation in the very early evolution of these fantastic objects. Here we first recall what are the main chemical properties of the long-lived low-mass stars observed today in GCs. Then we summarize the implications for the initial mass of the GCs, as well as for their contribution to field star populations and to cosmic reionisation. Finally we recall the detailed timeline proposed by Krause et al. (Astron Astrophys 546(L5) 2012, Astron Astrophys 552(A121) 2013) for the first 40 Myrs in the lifetime of a typical GC following the general ideas of our so-called “Fast Rotating Massive stars scenario” and taking into account the dynamics of interstellar bubbles produced by stellar winds and supernovae.