A possible trigger of the multiple population phenomenon in star clusters

Abstract

Multiple populations (MPs) is a intra-star cluster phenomenon consisting in star-to-star variation of the abundance of some light chemical elements. They have been observed in many star clusters, most of them old globular clusters, populating the Milky Way and other satellite galaxies. Since the study of MPs became more systematic, different astrophysical parameters have been claimed to be the main responsible for its occurrence. However, at the present time, no attempt would seem to have solved this conundrum. This work deals with a potential trigger of the MPs phenomenon, based on the gathered observational evidence of the existence of MPs in some star clusters and the absence of its in others. We found that star clusters with MPs mostly formed during time intervals of intense star formation activity in a galaxy, for instance during the galaxy formation epoch, a close galaxy encounter, etc. At those time intervals where relative peaks in the galaxy star formation rate occur, star clusters with masses above a lower mass limit harbour MPs. This lower star cluster mass limit would marginally depend on the star cluster age.