We’ve just discovered something remarkable: a cluster made of over 30 galaxies packed into a tiny area about 500,000 light-years wide. This formation dates back to just 1.4 billion years after the Big Bang and is surprisingly hotter than scientists expected.
Astronomers from Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) have labeled this star-studded group SPT2349-56. It pushes the boundaries of what we know about how quickly galaxies can come together. “This challenges what we thought about the speed of galaxy formation,” said Scott Chapman, an astronomy professor at Dalhousie University. He suggests that powerful energy output from supermassive black holes in the cluster may have influenced its growth sooner than anticipated.
Dazhi Zhou, a PhD candidate at the University of British Columbia and lead author of the study, calls the hot gas surrounding these galaxies the cluster’s “atmosphere.” Usually, this gas, termed the intracluster medium, can reach incredibly high temperatures—sometimes over 100 million degrees Celsius. Surprisingly, SPT2349-56’s gas is at least five times hotter than expected for such a young cluster. “We never expected to find this kind of heat so early in cosmic history,” Zhou comments.
Scientists measured this heat using a method called the Sunyaev–Zeldovich effect, which shows how galaxy clusters interact with cosmic microwave background (CMB) radiation—essentially the faint afterglow of the Big Bang. As CMB radiation enters the cluster, it interacts with electrons in this hot gas and gains energy. The more energetic the electrons, the hotter the cluster appears.
While clusters that formed earlier have been discovered, SPT2349-56 stands out because those earlier groups are still evolving and aren’t yet stable. In contrast, SPT2349-56 seems to have formed its structure more quickly, suggesting that our models of galaxy formation need revisiting.
Excitingly, SPT2349-56 features frenetic star formation. The galaxies within it are producing stars at a staggering rate—five thousand times faster than what we see in our Milky Way. “We want to understand how intense star formation and active black holes are influencing this hot atmosphere,” Zhou explains. “It’s amazing how all of this is happening together in such a young system.”
These findings, published in Nature, are part of an ongoing exploration into the universe’s early history, shedding light on how galaxies and clusters formed. As researchers delve deeper, we might uncover even more surprising truths about our cosmic beginnings.
