SO Webloquio: Multiple stellar populations in globular clusters: Properties, origin, open questions

Globular clusters (GCs) are fascinating objects nearly as old as the Universe that provide insight on a large variety of astrophysical and cosmological processes. However, their formation and their early dynamical evolution are far from being understood. In particular, the classical paradigm describing GCs as large systems of coeval stars formed out of chemically homogeneous material has been definitively swept away by recent high-precision spectroscopic and deep photometric observations. These data have provided undisputed evidence that GCs host multiple stellar populations, with very peculiar chemical properties. Evidence is also accumulating about the presence of multiple stellar populations in young massive star clusters in Local Group galaxies. In this talk, I will review the properties of these multiple populations, before presenting the different scenarios that have been proposed to explain their formation. I will focus on the (many) current theoretical issues and on the possible relationships between GCs and young massive star clusters observed in the local universe. I will conclude on open questions.