A young galaxy cluster observed in the early universe is surprisingly hot and abundant in gas, challenging scientists' models of how such structures evolve. Named SPT2349-56, the cluster's intracluster gas reaches temperatures of several tens of millions of degrees, far exceeding predictions. Researchers suggest active galaxies within it may be accelerating the heating process.
Astronomers have uncovered an anomaly in the early universe: the galaxy cluster SPT2349-56, located just 1.4 billion years after the big bang. This structure, observed using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, contains intracluster gas that is both more abundant and significantly hotter than expected for such a nascent formation.
Dazhi Zhou at the University of British Columbia in Canada led the team that detected temperatures of at least several tens of millions of degrees toward the cluster's center. "The temperature of the surface of the sun is a few thousand degrees Celsius, so this entire area is hotter than the sun," Zhou explained. Their calculations indicate the gas is 5 to 10 times hotter than simulations predicted, a surprise because such extreme heat was anticipated only billions of years later in cluster development.
"This kind of gas should still be cool and less abundant because these baby clusters are still accumulating and heating their gas," Zhou noted. SPT2349-56 appears unusually mature, potentially due to several active galaxies among its members. These include at least three emitting powerful energy jets, alongside frequent star formation bursts, which could rapidly elevate the gas temperature.
This discovery highlights a previously unseen phase in cluster evolution. "What this really does is open a new window showing a phase of cluster evolution that we have never seen before," Zhou said. The team plans further ALMA observations to search for similar hot, young clusters and assess their rarity. The findings, published in Nature, may reshape understandings of galaxy cluster formation in the universe's infancy.