The formation, disruption and properties of pressure-supported stellar systems and implications for the astrophysics of galaxies

TL;DR

This paper reviews the physical processes influencing the formation and evolution of dense stellar systems, highlighting how their properties change around 10^6 solar masses and implications for galaxy formation and dark matter evidence.

Contribution

It discusses the early and later dynamical evolution of dense stellar systems and their impact on galaxy properties, emphasizing the significance of relaxation times and mass thresholds.

Findings

Stellar populations become complex near 10^6 Msol.

A galaxy-like mass-radius relation emerges at higher masses.

Systems with relaxation times longer than a Hubble time show weak dark matter evidence.

Abstract

Most stars form in dense star clusters deeply embedded in residual gas. These objects must therefore be seen as the fundamental building blocks of galaxies. With this contribution some physical processes that act in the very early and also later dynamical evolution of dense stellar systems in terms of shaping their later appearance and properties, and the impact they have on their host galaxies, are highlighted. Considering dense systems with increasing mass, it turns out that near 10^6 Msol their properties change fundamentally: stellar populations become complex, a galaxial mass--radius relation emerges and the median two-body relaxation time becomes longer than a Hubble time. Intriguingly, only systems with a two-body relaxation time longer than a Hubble time show weak evidence for dark matter, whereby dSph galaxies form total outliers.