Astronomers discover clusters galaxy the earliest and hottest ever observed in the universe. The cluster named SPT2349-56 was detected 1.4 billion years after Big Bang This indicates conditions that are much more mature and hotter than predicted by the theory of galaxy cluster formation.
Quoting Space on January 8, 2026, the cluster consisted of more than 30 galaxies squeezed into a region about 500 thousand light years in diameter. This extreme density and temperature are considered unusual for a galaxy cluster of this age, challenging scientists’ understanding of how quickly galaxies and galaxy clusters can form and evolve.
The research was published on January 5 in the journal ‘Nature’ running at the Atacama Large Millimeter/submillimeter Array (ALMA) economic observatory in Chile. According to the researchers, the extreme conditions of SPT2349-56 indicate the existence of a large energy source in the early universe, which then influenced the formation of the cluster.
“This tells us that something in the early universe, possibly three newly discovered supermassive black holes in this cluster, was already pumping enormous amounts of energy into the surrounding environment,” said Scott Chapman, a professor of astronomy at Dalhousie University, Canada, in a review Space.
Galaxy clusters are generally enveloped in hot gas known as the intercluster medium, which functions like an atmosphere. In today’s galaxy clusters, the temperature of this medium can reach tens to hundreds of millions of degrees Celsius. So far, astrophysicists believe it will take billions of years for the gas to heat up to that level. An examination of SPT2349-56 shows otherwise.
“We didn’t expect to see such a hot cluster atmosphere at such an early phase in cosmic history,” said Dazhi Zhou, a University of British Columbia doctoral student and lead author of the study. “This gas was at least five times hotter than predicted, even hotter and more energetic than many galaxy clusters today.”
The temperature of the SPT2349-56 intercluster medium is measured indirectly through effects Sunyaev–Zeldovich—changes in the cosmic microwave background radiation (CMB) as its photons interact with hot electrons in galaxy clusters. The hotter the gas, the more energy is transferred to the CMB photons, so cluster traces can be detected.
In this cosmically old galaxy cluster, researchers also examined protoclusters that formed 650–770 million years after the Big Bang. These clusters are not completely gravitationally bound and do not have a high temperature intercluster medium. In contrast, SPT2349-56 appears to be growing rapidly, indicating that current models of galaxy cluster formation do not fully explain this early heating process.
A similarity between SPT2349-56 and other early protoclusters is their extremely high star formation rate. Small galaxies in this cluster form stars up to thousands of times faster than the Milky Way. “We want to understand the very intense process of star formation, the activity of black holes, and their interactions with this overheated atmosphere,” said Zhou.
