A cosmological framework for stellar collisions at high redshift in proto-globular clusters, nuclear star clusters, and Little Red Dots

TL;DR

This paper presents an analytic framework for stellar collisions in early high-density stellar systems, linking cosmological initial conditions to observable outcomes, validated by simulations.

Contribution

It introduces a comprehensive, radially-resolved model connecting cosmological initial conditions to stellar collision outcomes in dense environments.

Findings

Stellar collisions are common in high-redshift dense stellar systems.

Runaway collisions can produce very massive stars early in cosmic history.

High collision rates can create dense gaseous environments around black holes.

Abstract

Observations and cosmological simulations indicate that the early Universe hosted numerous compact, high-density stellar systems, where close encounters and physical collisions between stars were likely common. We develop a bottom-up framework for stellar dynamics in such environments, spanning systems with and without intermediate- and supermassive black holes, and covering regimes where stellar collisions may or may not dominate the evolution. This radially-resolved analytic model connects dense star clusters in their cosmological context to observable outcomes mediated by stellar collisions. Initial conditions and environmental properties are drawn from high-resolution cosmological simulations, enabling exploration across a broad region of parameter space. The analytic predictions are validated against Monte Carlo simulations, demonstrating good agreement across key regimes. We find that stellar collisions are ubiquitous in many high-redshift environments, with runaway sequences naturally leading to the formation of very massive stars at early times. Finally, we show that high rates of destructive collisions can rapidly build up extremely dense gaseous environments around massive black holes, potentially providing an analogue to the observed population of Little Red Dots.