Earliest, hottest galaxy cluster gas on record could change cosmological models

An international team of astronomers led by Canadian researchers 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, far earlier and hotter than theory predicts. 

The result, published today in Nature, could upend current models of galaxy cluster formation, which predict such temperatures occur only in more mature, stable galaxy clusters later in the universe’s life. 

“We didn’t expect to see such a hot cluster atmosphere so early in cosmic history,” said lead author Dazhi Zhou, a PhD candidate in the UBC department of physics and astronomy. “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.” 

“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,” said co-author Dr. Scott Chapman, a professor at Dalhousie University who conducted the research while at the National Research Council of Canada (NRC). 

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), which includes instruments designed, built, and tested by the NRC. 

This infant cluster is massive for its relative youth, with a core measuring about 500,000 light years across, comparable to the size of the halo surrounding the Milky Way. It contains more than 30 active galaxies and 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, which can help scientists work out the thermal energy of the intracluster medium: the gas existing between the galaxies of a given cluster. 

“Understanding galaxy clusters is the key to understanding the biggest galaxies in the universe,” said Dr. Chapman, who is also a UBC affiliate professor. “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 blackhole heating 

​Current models suggest the massive reservoirs of gas that form the intracluster medium are collected, and then heated, by gravitational interactions as an immature, unstable galaxy cluster matures and collapses inward to a stable state. The new finding suggests that 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. “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,” said Zhou. “How can all of this be happening at once in such a young, compact system?”