Abstract

Contributed Talk - Splinter StarClusters   (MW-2050)

From Million-Body Star Clusters over Cosmic Time to Black Hole Growth in Primordial Systems

Kai Wu, Rainer Spurzem, Philip Cho, Francesco Flammini Dotti, Ataru Tanikawa, Albrecht Kamlah
ARI/ZAH, Universität Heidelberg

We present recent progress from two independent but complementary studies of dense star-cluster evolution across cosmic environments. The main focus of this contribution is the DRAGON-III project, a new suite of direct $N$-body simulations of million-body globular clusters and nuclear star clusters evolved over 10 Gyr. Building on DRAGON-II, which linked cluster dynamics, stellar evolution, and compact-object mergers, DRAGON-III extends star-by-star modelling to more massive and astrophysically relevant systems. The project aims to resolve the coupled effects of two-body relaxation, mass segregation, binary interactions, compact-remnant production, and, in nuclear clusters, the dynamical influence of central massive black holes. These simulations connect internal cluster evolution to observable structural properties, tidal disruption activity, and gravitational-wave source populations. We also briefly report results from a separate study of extremely massive Population III star clusters, based on eight direct $N$-body simulations with $1.01 imes10^5$ stars, primordial binaries, top-heavy initial mass functions, and varying initial bulk rotation. These models show that rotation accelerates gravothermal collapse and promotes intermediate-mass black hole formation through both stellar-collision and black-hole merger channels, while relativistic recoil kicks can suppress hierarchical growth. Together, these studies demonstrate the power of direct $N$-body simulations to probe dense stellar systems from primordial clusters to present-day globular and nuclear clusters.