Abstract
<title>Abstract</title> <p>Globular clusters (GCs) are among the oldest and densest stellar systems in the Universe, but how they formed remains uncertain. Their small sizes, high stellar densities and old ages imply that they must have assembled rapidly in the early Universe, yet cosmological simulations have so far been unable to resolve their internal dynamical structure at birth. Here we show, using cosmological simulations with sub-parsec resolution in which stars are formed individually, that a compact stellar system with GC-like mass and size can form at redshift z = 10.5 in a single, short-lived event. For the first time in a fully cosmological simulation, the internal dynamical structure of a forming proto–GC is directly resolved, allowing its angular momentum and rotational support to be followed during assembly. The system assembles most of its stellar mass within a few Myr, rapidly becomes gas-poor and star-dominated, and develops ordered internal rotation. Its density, size and mass overlap with those of compact stellar systems recently observed by JWST at high redshift. These results indicate that GCs can emerge as dynamically structured stellar systems already at birth, and that their internal kinematics may preserve a fossil record of the physical conditions under which they formed.</p>