Formation of Very Young Massive Clusters and Implications for Globular Clusters

Abstract

How Very Young Massive star Clusters (VYMCs; also known as "starburst" clusters), which typically are of 10 4 M and are a few Myr old, form out of Giant Molecular Clouds is still largely an open question. Increasingly detailed observations of young star clusters and star-forming molecular clouds and computational studies provide clues about their formation scenarios and the underlying physical processes involved. This chapter is focused on reviewing the decadelong studies that attempt to computationally reproduce the well-observed nearby VYMCs, such as the Orion Nebula Cluster, R136 and NGC 3603 young cluster, thereby shedding light on birth conditions of massive star clusters, in general. On this regard, focus is given on direct N-body modeling of real-sized massive star clusters, with a monolithic structure and undergoing residual gas expulsion, which have consistently reproduced the observed characteristics of several VYMCs and also of young star clusters, in general. The connection of these relatively simplified model calculations with the structural richness of dense molecular clouds and the complexity of hydrodynamic calculations of star cluster formation is presented in detail. Furthermore, the connections of such VYMCs with globular clusters, which are nearly as old as our Universe, is discussed. The chapter is concluded by addressing long-term deeply gas-embedded (at least apparently) and substructured systems like W3 Main. While most of the results are quoted from existing and up-to-date literature, in an integrated fashion, several new insights and discussions are provided.

How Initial Size Governs Core Collapse in Globular Clusters

“…In particular, residual gas expulsion could lead to significant cluster expansion at early times, attenuating the long-term dynamical processing of BHs and thus altering the structural features of the clusters at late times. However, several recent analyses (e.g., Brinkmann et al 2017;Banerjee & Kroupa 2018) have shown that the early stages of formation of some clusters may feature a substantially more compact embedded phase of sub-pc length scale, comparable to the thickest molecular-cloud filaments, from which a substantial gas dispersal would result in sizes comparable to those of the initial configurations considered here and also of the observed gas-free young massive clusters, as demonstrated in Figure 1. While such processes may be important, they are beyond the scope of this analysis.…”

Stellar-mass black holes in young massive and open stellar clusters – IV. Updated stellar-evolutionary and black hole spin models and comparisons with the LIGO-Virgo O1/O2 merger-event data

“…3.1). It is clear that with increasingly improved constraints on (differential) compact-binary merger rate density from LVK observations, it would be possible to provide constraints on widely debated issues regarding star cluster formation and large scale structure formation, e.g., mass dependence of cluster formation efficiency, R mort (M cl ), and lower and upper mass limits, [M GC,low , M GC,high ], of GC progenitors (see, e.g., Rodriguez et al 2015;Banerjee & Kroupa 2018;Kruijssen et al 2019;El-Badry et al 2019;Krumholz et al 2019). The differential merger rate density profiles would also help constraining the relative contributions of the various other channels for producing compact binary mergers, e.g., dynamical evolution of field hierarchical systems, mergers via Kozai-Lidov mechanism in galactic nuclei, and evolution of field massive binaries.…”

The Dawes Review 8: Measuring the Stellar Initial Mass Function

“…In contrast, there is evidence for monolithic collapse in the formation of some young Galactic star clusters (e.g. Banerjee & Kroupa 2014, 2015, 2018).…”