An ancient galaxy cluster is displaying temperatures far above what it should have been capable of producing, prompting astronomers to reconsider our models about the early universe.
Designated SPT2349-56, gases within the galaxy cluster far exceed the temperatures expected from a cluster that came into existence just 1.4 billion years after the Big Bang. The discovery, made by a Canadian-led international team, was reported in a paper published in Nature.
Witnessing the Unexpected
“We didn’t expect to see such a hot cluster atmosphere so early in cosmic history,” said lead author Dazhi Zhou, a PhD candidate at the University of British Columbia. “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.”
Despite Zhou’s initial skepticism, the team’s confirmations support something much more explosive occurring in the remote galactic past than was previously expected.
“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.
Viewing a Galaxy Cluster
As technologies that enable modern astronomical observation continue to improve, scientists can resolve signals from increasingly distant regions of the universe. Because the speed of light is constant, these observations not only reveal what’s out there in the cosmos; they also effectively allow us to see back in time, as signals from distant regions take a long time to reach us here on Earth.
In the case of the galaxy cluster SPT2349-56, a so-called “baby” cluster, the observations astronomers are now making involve signals that were originally generated roughly 12 billion years ago.
The observations were made possible with the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile, which consists of 66 antennas at an elevation of 16,000 feet, positioned relatively close to the equator. Along with data collected by ALMA, researchers employed what is known as the Sunyaev-Zeldovich effect, which traces the distortion of the cosmic microwave background caused by galaxy clusters, to determine the temperature of the gas within SPT2349-56, known as the intracluster medium.
“Understanding galaxy clusters is the key to understanding the biggest galaxies in the universe,” said Dr. Chapman. “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.”
An Infant Galaxy Cluster
SPT2349-56 is extremely massive, despite its relative youth, and contains 30 active galaxies. Its core, approximately 500,000 light-years wide, is roughly the size of our galaxy’s halo. Within that compact space, the galaxy cluster hosts stars that are formed at a rate roughly 5,000 times that of the Milky Way.
Prior to observing SPT2349-56, models indicated that gravitational interactions in immature, unstable galaxies drive the accumulation and heating of the intracluster medium as the cluster moves toward greater stability. Instead of the slow, gradual buildup predicted by these models, the data suggests to astronomers that something much quicker and more explosive is collecting and heating the intracluster medium.
“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,” Zhou said.
“How can all of this be happening at once in such a young, compact system?” Zhou added.
Fundamentally, such an observation offers ample reason for astronomers to reconsider current models of galaxy cluster evolution, and the research team now says it plans to continue its investigations into the surprising levels of activity observed in the early universe.
The team’s paper, “Sunyaev-Zeldovich Detection of Hot Intracluster Gas at Redshift 4.3,” appeared in Nature on January 5, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.