Recent analyses of the nascent celestial grouping SPT2349-56, conducted with the Atacama Large Millimeter/submillimeter Array (ALMA), have brought to light remarkably heated gas within the cluster mere 1.4 billion years post-Big Bang, thereby presenting a significant challenge to prevailing theories of galaxy cluster development.
An artist’s impression of the forming galaxy cluster SPT2349-56: radio jets from active galaxies embedded in a hot intracluster atmosphere (red), illustrating a large thermal reservoir of gas in the nascent cluster. Image credit: Lingxiao Yuan.
SPT2349-56 is situated at a cosmic distance of approximately 12.4 billion light-years, signifying that the light we observe originated when the cosmos was merely 1.4 billion years old, representing about one-tenth of its current age.
At the heart of this protocluster, a dense core is observed to contain numerous rapidly expanding supermassive black holes alongside upwards of 30 galaxies undergoing intense star formation.
These galaxies are prodigious star factories, producing stars at rates potentially 1,000 times greater than that of our own Milky Way, and are congregated within a spatial volume only roughly three times the diameter of the Milky Way.
“We did not anticipate encountering such a highly energized cluster atmosphere so early in the universe’s timeline,” stated Dazhi Zhou, a doctoral candidate affiliated with the University of British Columbia.
The astronomical investigation employed a distinctive observational methodology known as the thermal Sunyaev-Zel’dovich (tSZ) effect.
This phenomenon detects not the emission from the gas itself, but rather a subtle dimming effect caused by energetic electrons within galaxy clusters interacting with the residual radiation from the Big Bang, observed as the Cosmic Microwave Background.
Prior to this recent finding, it was widely presumed that in the early epochs of the cosmos, galaxy clusters had not yet reached sufficient maturity to have fully developed and consequently heated their internal gas.
No instances of hot cluster atmospheres had been directly identified within the initial 3 billion years of cosmic existence.
“SPT2349-56 fundamentally alters our previous understanding,” commented Professor Scott Chapman, a researcher associated with Dalhousie University and the University of British Columbia.
“Our measurements reveal a significantly heated cluster atmosphere at just 1.4 billion years after the Big Bang, a period when we believed the intracluster gas should still be relatively cool and in the process of gradual aggregation.”
“This suggests that the formation of massive clusters may involve a far more energetic and efficient process of gas heating than our current theoretical frameworks have posited.”
According to the research findings, potent energetic outflows emanating from SPT2349-56’s supermassive black holes, manifesting as luminous radio galaxies, might serve as a natural mechanism for the infusion of the immense energy required to superheat the intracluster gas at such an early cosmic stage.
This revelation implies that during the Universe’s formative first billion years, energetic phenomena, such as bursts from supermassive black holes and vigorous star formation events, could have profoundly elevated the temperature of the surrounding gas within developing clusters.
This phase of intense heating may have been critical in the metamorphosis of these initially cooler, nascent galaxy clusters into the vast, hot structures observed in later cosmic eras.
Furthermore, it indicates a need for revisions to contemporary models concerning the developmental trajectories of galaxies and their surrounding environments.
This represents the earliest confirmed direct detection of hot cluster gas, effectively extending the observational frontier for studying these cosmic environments further back in time.
The discovery confirming the existence of massive reservoirs of superheated plasma at such an early juncture compels a reevaluation by the scientific community regarding the chronological order and the pace of galaxy cluster evolution.
It also introduces new avenues of inquiry into the specific roles that supermassive black holes and galaxy formation play in shaping the broader cosmic landscape.
“SPT2349-56 presents us with a truly anomalous and captivating observational arena,” remarked Zhou.
“We are observing intense stellar genesis, active supermassive black holes, and this exceptionally heated atmosphere, all concentrated within a young, compact cluster.”
“A substantial observational void persists between this tumultuous early phase and the more quiescent clusters we observe in later cosmic periods.”
“Charting the evolutionary path of their atmospheres across cosmic time promises to be a highly compelling area for future scientific endeavors.”
The findings were formally published on January 5, 2026, in the esteemed scientific journal Nature.
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D. Zhou et al. Sunyaev-Zeldovich detection of hot intracluster gas at redshift 4.3. Nature, published online January 5, 2026; doi: 10.1038/s41586-025-09901-3
