Star Cluster Evolution: Near and Far, Large and Small, Old and Young

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Star clusters are self-gravitating groups of stars with the same distance, age, and chemical composition. Stars are naturally formed in clustered environments, but only a few of those clusters will emerge as a self-contained, gravitatationally-bound entity from their natal molecular cloud. Nevertheless, the presence of close neighbours during the star formation process has important consequences for the masses and multiplicity of the stars that can form, and the survivability of planetary systems. Of those clusters that do emerge as clearly-identifiable objects, some will become massive old globular clusters. They have survived the entire galaxy formation process, including those times when two galaxies merged, or when a dwarf galaxy falls into its larger host galaxy. We can use the present-day properties of star clusters (size, mass, position, velocities, stellar content) to map galaxy structure and assembly over the last 10 billion years. But in order to use clusters to learn about star formation, planet formation or galaxy evolution, we need to understand how the clusters themselves form and change with time. The mature field of stellar dynamics (how stars move under their mutual gravity) provides many of the answers. However, stellar dynamics alone is not sufficient. It is important to also consider the interaction between the stars and star cluster with their external environment, such as the gas from which the stars formed, or the tidal field of the galaxy in which the cluster resides. The proposal describes a research program that will address these issues. In the next five years, we will concentrate on three specific projects: 1) to simultaneously and self-consistently model the formation and evolution of star clusters, their gas content, and their stellar populations, starting from the deeply embedded phase in molecular clouds, to produce the spherical, gas-free, open and globular clusters we see in the Milky Way today. 2) to trace the dynamical evolution of globular clusters and nuclear star clusters in their host galaxy, including episodes of galaxy mergers. In particular, we will quantify any observational signatures of accretion and merging on the individual clusters and the cluster populations as an ensemble. 3) to predict the expected observational signatures of the present-day massive old clusters as they are forming in the very early universe. Through simulations that combine stellar evolution, stellar dynamics, and hydrodynamics, we will produce a comprehensive picture of cluster formation and evolution on many scales of time, size, and distance.