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- Astronomers have discovered the earliest, hottest galaxy cluster gas yet. The active galaxies in this early universe cluster have jets that spew hot gas into space, creating a gas cloud that surrounds them.
- The scorching cloud of gas threaded between clusters of galaxies is five times hotter than current models predict. Astronomers did not expect such active, hot gas around galaxies only 1.4 billion years after the Big Bang.
- The discovery highlights gaps in our models of galaxy cluster formation. The researchers want to know what this early activity tells us about how present galaxy clusters formed.
The University of British Columbia posted this original story on January 5, 2026. Edits by EarthSky.
Earliest, hottest galaxy cluster gas could upend models
An international team of astronomers led by Canadian researchers said on January 5, 2026, that it has found something the universe wasn’t supposed to have: a galaxy cluster blazing with hot gas just 1.4 billion years after the Big Bang. That’s far earlier and hotter than theory predicts.
The peer-reviewed journal Nature published the result on January 5, 2026. The discovery could upend current models of galaxy cluster formation. These models predict that such temperatures occur only in more mature, stable galaxy clusters later in the universe’s life.
Lead author Dazhi Zhou of the University of British Columbia said:
We didn’t expect to see such a hot cluster atmosphere so early in cosmic history. In fact, at first I was skeptical about the signal as it was too strong to be real. But after months of verification, we’ve confirmed this gas is at least five times hotter than predicted, and even hotter and more energetic than what we find in many present-day clusters.
Co-author Scott Chapman of Dalhousie University said:
This tells us that something in the early universe, likely three recently discovered supermassive black holes in the cluster, were already pumping huge amounts of energy into the surroundings and shaping the young cluster, much earlier and more strongly than we thought.
Investigating a baby cluster
Peering back in time about 12 billion years, the researchers focused on a ‘baby’ galaxy cluster called SPT2349-56. To do so, the research team used a cluster of radio telescopes called the Atacama Large Millimeter/submillimeter Array (ALMA).
This infant cluster is massive for its relative youth, with a core measuring about 500,000 light-years across. That’s comparable to the size of the halo surrounding the Milky Way. It contains more than 30 active galaxies. And it forms stars more than 5,000 times faster than our own galaxy, all in a very compact region.
The research team focused on a cosmological tool called the Sunyaev-Zeldovich effect. This effect can help scientists work out the thermal energy of the intracluster medium: the gas existing between the galaxies of a given cluster.
Chapman said:
Understanding galaxy clusters is the key to understanding the biggest galaxies in the universe. These massive galaxies mostly reside in clusters, and their evolution is heavily shaped by the very strong environment of the clusters as they form, including the intracluster medium.
Supermassive black hole heating
Current models suggest the massive reservoirs of gas that form the intracluster medium are collected, and then heated, by gravitational interactions. This happens as an immature, unstable galaxy cluster matures and collapses inward to a stable state. The new finding suggests this birth is more explosive, and that scientists may need to rethink the sequence and speed of galaxy cluster evolution.
The researchers now want to investigate how all the pieces fit together. Zhou said:
We want to figure out how the intense star formation, the active black holes and this overheated atmosphere interact, and what it tells us about how present galaxy clusters were built. How can all of this be happening at once in such a young, compact system?
Bottom line: Astronomers have discovered the earliest, hottest galaxy cluster gas yet. This scorching gas between galaxies is much hotter than predicted for so early in the universe.
Source: Sunyaev–Zeldovich detection of hot intracluster gas at redshift 4.3
Via University of British Columbia