Feedback-Free Star Formation in Clusters within a Galaxy Simulated at High Resolution in Cosmic Dawn

We perform a cosmological zoom-in simulation of a massive galaxy (Mₛ~ 10¹⁰ M_ at z ∼ 10) using the GIZMO code. By employing ≤ 3 pc resolution and a 3.4 Myr supernova feedback delay, we capture the feedback-free starbursts (FFB) in clusters. The simulation reproduces FFB model predictions and super-bright galaxies observed by JWST. At z ∼ 10, cold streams feed a compact galaxy (Rₑ~ 1 kpc), with stellar and surface densities (>10⁵ cm⁻³, >10⁵ M_ pc⁻²) exceeding FFB thresholds. The global star-formation efficiency (SFE) is ϵs ∼ 0.2–0.3, associated with a fluctuating star-formation history. We identified over 105 star clusters (M>104.5 M_) with a nearly scale-free mass distribution (dN/dlog M∝M−1.06). Approximately 90% of star formation occurs in clusters, which at a given time constitute 30\!-\!40~\ per\ cent of the total stellar mass. The star formation in most of the clusters of masses <10⁷ M_, occurs in bursts of <3 Myr and a local SFE ∼0.5 ± 0.2. Cluster metallicities (−2.01 < log (Z/Z⊙) < −0.45) indicate rapid baryon recycling. Feedback-driven outflows exhibit typical temperature of 10⁷ K and typical velocities of ~ 2000 km\ s⁻¹. In the highly dynamic central 1 kpc, clusters undergo rapid orbital decay and merge to assemble the oblate nuclear stellar cluster. Cluster shapes range from oblate to prolate, with a triaxial median. These clusters are consistent with JWST observations, and a fraction of them may survive to yield the globular clusters (GCs) at low redshifts.