JWST Reveals Surprisingly Complex Galaxy Merger System in Early Universe
The James Webb Space Telescope (JWST) has upended existing cosmological models with the discovery of a system of five interacting galaxies that existed just 800 million years after the Big Bang. This finding challenges the long-held belief that galaxies in the early universe were largely isolated and less massive, forcing astronomers to reconsider the timeline of galactic evolution.
A Cosmic Collision Earlier Than Expected
Galaxy mergers are a fundamental process in the universe, believed to be crucial for the formation of the large galaxies we observe today, including our own Milky Way. Prior to the JWST’s observations, the prevailing theory suggested that significant galaxy mergers were uncommon until more than one billion years after the universe’s birth. However, the JWST is consistently revealing that the early universe was a far more dynamic and chaotic place than previously imagined.
The discovery, detailed in new research published in Nature Astronomy titled “Extended enriched gas in a multi-galaxy merger at redshift 6.7,” is led by Dr. Weida Hu, a post-doctoral researcher at Texas A&M University. The research team uncovered evidence of multiple star-forming clumps within the system, strongly indicating ongoing mergers.
“Recent JWST observations have uncovered high-redshift galaxies characterized by multiple star-forming clumps, many of which appear to be undergoing mergers,” the authors write. This observation clashes with the expectation of a more sparsely populated early universe. Such mergers, particularly those involving galaxies of comparable mass, are critical for driving galaxy evolution and shaping the chemical composition of their environments.
The five-galaxy merger has been dubbed JWST’s Quintet (JQ). “What makes this remarkable is that a merger involving such a large number of galaxies was not expected so early in the universe’s history, when galaxy mergers were thought to be simpler and usually involve only two to three galaxies,” Dr. Hu explained in a press release.
A Hotbed of Star Formation and Ionized Gas
Despite the vast distances – tens of thousands of light-years – separating the galaxies within JQ, they are remarkably tightly packed. The system also exhibits an exceptionally high star formation rate (SFR) of approximately 250 solar masses per year. This rate is particularly noteworthy for galaxies in the early universe, where abundant pristine gas fueled rapid star birth.
Beyond the unexpected merger itself, the JWST detected a significant amount of ionized oxygen being generated and dispersed into the circumgalactic medium (CGM) surrounding JQ. “We also detect a large [O iii] + Hβ gaseous halo surrounding and connecting four galaxies in JQ, suggesting the existence of metals in the surrounding medium—the inner part of its circumgalactic medium,” the authors write. [O iii] – doubly-ionized oxygen – indicates powerful radiation has stripped electrons from oxygen atoms. By analyzing the ratio of [O iii] to hydrogen, astronomers can infer the source of this radiation, which the researchers believe originates from shocks generated by the merging galaxies.
“It is therefore more plausible that the [O III]+Hβ halo of JQ results from oxygen-enriched gas stripped out of the galaxies through interactions and tidal forces,” the researchers explain. “The stripped gases are shock-heated in galaxy collisions and dispersed to large radii, leading to large hot gaseous halos.”
[Image of JQ galaxies and the [O iii] + Hβ cloud would be inserted here. Image Credit: Hu et al. 2026 NatAstr]
A Potential Link to Quiescent Galaxies
This discovery also sheds light on another recent puzzle: the existence of surprisingly massive, yet quiescent galaxies – galaxies that have largely ceased star formation – observed just 1 to 1.5 billion years after the Big Bang. The rapid formation of stars in these galaxies was previously difficult to explain given the limited time available in the early universe.
The JQ system could represent a precursor to these quiescent galaxies. Its substantial mass and high SFR align with the star formation history needed to explain their existence. “The high mass and star formation rate of JQ are consistent with the star formation history of those unexpected massive quiescent galaxies observed at redshift 4–5, offering a plausible evolutionary pathway for the formation of such galaxies,” the authors explain.
[Image showing JQ as a precursor to quiescent galaxies would be inserted here. Image Credit: Hu et al. 2026 NatAstr]
Rewriting the Rules of Galactic Assembly
The JWST’s ongoing stream of groundbreaking observations underscores the importance of challenging existing theories. As one researcher noted, if observations always confirmed existing models, it would signal a flaw in the scientific process itself. The telescope is consistently delivering unexpected findings, prompting scientists to refine their understanding of the cosmos.
“By showing that a complex, merger-driven system exists so early, it tells us our theories of how galaxies assemble — and how quickly they do so — need to be updated to match reality,” said co-author Dr. Casey Papovich, a Professor of Physics and Astronomy at Texas A&M University. The JWST is not simply confirming what astronomers already knew; it is actively rewriting the story of the universe’s origins and evolution.
