JWST observations show that distant massive galaxies contain far more small stars than expected, raising their estimated masses by a factor of up to four compared with initial measurements. Nature Astronomy published the peer-reviewed findings on August 21, 2026. The revised mass estimates suggest that early massive galaxies might be heavier than previously found, presenting a challenge to existing galaxy formation models.
The research, conducted by C. M. Cheng and colleagues, fitted new JWST data using stellar population models to examine bottom-heavy initial mass functions. Ground-based spectral data from the Large Early Galaxy Astrophysics Census (LEGA-C) data release 3, authored by A. van der Wel and collaborators, supplemented the space telescope measurements with 3,000 spectra of Ks-selected galaxies at redshifts greater than 0.6.
Researchers fitted the observational data using low-mass star counting models developed by C. Conroy and P. van Dokkum in 2012, along with 2018 model updates that account for metal-rich and metal-poor old stellar systems. In 2024, van Dokkum and Conroy published an alternative formulation for the proportion of small and large stars to help lower inferred masses. The new findings build on earlier work by C. L. Steinhardt and colleagues, who introduced the impossibly early galaxy problem in 2016, and the 2024 JWST EXCELS survey by A. C. Carnall and co-authors covering ultra-massive quiescent galaxies at redshifts between 3 and 5.
Springer Nature published the study under DOI 10.1038/s41550-026-02947-x. The publisher listed individual PDF access to the full paper for $39.95, alongside a 30-day Nature+ access option for $32.99 and an annual journal subscription for $119.00.
