Primordial rotating disk composed of at least 15 dense star-forming clumps at cosmic dawn

Abstract

Early galaxies form through dark matter and gas assembly, evolving into dynamically hot, chaotic structures driven by mergers and feedback. By contrast, remarkably smooth, rotating disks are observed in massive galaxies only 1.4 billion years after the Big Bang, implying rapid dynamical evolution. Probing this evolution mechanism necessitates studies of young galaxies, yet efforts have been hindered by observational limitations in both sensitivity and spatial resolution. Here we report high-resolution observations of a strongly lensed, quintuply imaged, low-luminosity young galaxy at redshift z = 6.072, just 930 million years after the Big Bang. Magnified by gravitational lensing, the galaxy resolves into at least 15 star-forming clumps (effective radii ~10-60 pc), dominating ~70% of the galaxy's ultraviolet flux. Cool gas emission reveals an underlying rotating disk (rotational-to-random motion ratio 3.58 ± 0.74) in a gravitationally unstable state (Toomre Q ≈ 0.2-0.3) with high surface gas densities comparable to local starbursts (~103‒5 M☉ pc‒2). These properties suggest that disk instabilities with weak feedback drive prolific clump formation. The extreme clumpiness surpasses galaxies at later epochs and current simulation predictions. Our findings directly connect small-scale internal structures, underlying disk dynamics along with feedback effects at cosmic dawn, potentially explaining the abundance of luminous galaxies observed in the early Universe.