Ten-Billion-Year Mystery How Galaxies Shape Themselves

The James Webb Space Telescope (JWST) has resolved a 10-billion-year mystery about how galaxies shape themselves by providing unprecedented detail on the internal structure and formation history of galaxies across cosmic time. JWST findings have significantly altered our understanding of galaxy formation timelines by revealing that galaxies formed and evolved much faster and earlier than previously thought.
 
JWST detected massive, bright galaxies existing just a few hundred million years after the Big Bang, far earlier and more developed than standard models predicted. This suggests that galaxy assembly and star formation were highly efficient in the early universe, requiring a re-evaluation of how quickly matter could collapse into galaxies. Observations show that thin stellar disks were already present in some galaxies as early as 8 billion years ago, much earlier than expected. The process of forming thick disks from turbulent gas, followed by the emergence of thin disks as turbulence subsides, appears to have occurred on different timescales depending on galaxy mass; faster in massive galaxies and slower in low-mass ones. Furthermore, the presence of large, bright, and mature galaxies in the early universe challenges the widely accepted Cold Dark Matter model, prompting consideration of alternative models such as Modified Newtonian Dynamics, which predicts rapid galaxy formation without the need for dark matter. Some findings even suggest that the interplay between black holes and star formation was more immediate and interconnected than previously believed, with black holes and stars co-evolving from the earliest epochs. JWST’s discoveries have sparked debate about whether fundamental aspects of cosmology, such as the behavior of dark energy, the efficiency of star formation, and the growth of dark matter halos, need to be revised to accommodate these early, massive galaxies.
 
These discoveries challenge and refine existing models of galaxy formation, suggesting that galaxies assembled their iconic disk structures much earlier and more dynamically than previously thought. The JWST’s sharp vision and ability to probe the motion of gas and stars have been crucial in uncovering these structural secrets, fundamentally advancing our understanding of how galaxies like our own Milky Way came to be. This is forcing astronomers to rethink galaxy formation timelines and the physical processes driving them.
 
References
Mann, A. (2023, August 2). The James Webb Space Telescope prompts a rethink of how galaxies form. Proceedings of the National Academy of Sciences of the United States of America.

Williams, E. (2025, June 30). James Webb Telescope Unlocks the Deep Structural Secrets of Disk Galaxies, Revealing How the Universe Built Its Greatest Shapes. Rude Baguette. 
 
(2025, June 30). JWST unlocks 10-billion-year mystery of how galaxies shape themselves. Tohoku University. Science Daily. 
https://www.sciencedaily.com/releases/2025/06/250629033347.htm