Rotating supermassive Pop III stars on the main sequence

¹ Department of Astronomy, University of Virginia, 530 McCormick Rd, Charlottesville, VA 22904, USA
² STAR Institute, Université de Liège, Liège, Belgium
³ Institute of Cosmology and Gravitation, Portsmouth University, Dennis Sciama Building, Portsmouth PO1 3FX, UK
⁴ Centre for Astrophysics and Space Sciences Maynooth, Department of Physics, Maynooth University, Maynooth, Ireland
⁵ Department of Physics & Astronomy, Allen Building, 30A Sifton Rd, University of Manitoba, Winnipeg MB R3T 2N2, Canada
⁶ Dept. of Space, Earth and Environment, Chalmers Univ. of Technology, Gothenburg, Sweden

^⋆ Corresponding author.

Received: 9 June 2025
Accepted: 1 August 2025

Abstract

The detection of billion-solar-mass supermassive black holes (SMBHs) within the first billion years of cosmic history challenges conventional theories of black hole formation and growth. Simultaneously, recent JWST observations revealing exceptionally high nitrogen-to-oxygen abundance ratios in galaxies at high redshifts raise critical questions about rapid chemical enrichment mechanisms operating in the early universe. Supermassive stars (SMSs) with masses of 1000–10 000 M_⊙ are promising candidates to explain these phenomena, but existing models have so far neglected the pivotal role of stellar rotation. Here we present the first comprehensive evolutionary models of rotating Pop III SMSs computed using the GENEC stellar evolution code, including detailed treatments of rotation-induced chemical mixing, angular momentum transport, and mass loss driven by the ΩΓ limit. We demonstrate that rotation significantly enlarges the convective core and extends stellar lifetimes by up to 20%, with moderate enhancement of mass-loss rates as stars approach critical rotation thresholds. Our results further indicate that the cores of SMSs rotate relatively slowly (below ∼200 km s⁻¹), resulting in dimensionless spin parameters a * < 0.1 for intermediate-mass black hole (IMBH) remnants that are notably lower than theoretical maximum spins. These findings highlight rotation as a key factor in determining the structural evolution, chemical yields, and black hole spin properties of SMSs, and provide critical insights into the observational signatures from the high-redshift universe and their interpretation.