Weird clump in the early universe is piping hot and we don’t know why

A young galaxy cluster in the early universe is defying our understanding of how these huge structures formed and evolved. The gas that fills this cluster, called SPT2349-56, is far hotter and more abundant than it should be, and researchers aren’t sure why.

Dazhi Zhou at the University of British Columbia in Canada and his colleagues observed the cluster using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and found that towards its centre, the intracluster gas has a temperature of at least several tens of millions of degrees.

“The temperature of the surface of the sun is a few thousand degrees Celsius, so this entire area is hotter than the sun,” says Zhou. “From our conservative calculation, it is 5 to 10 times hotter than expected based on simulations – that is very surprising because this kind of hot gas was expected to exist only billions of years later.”

SPT2349-56 is located in the early universe, about 1.4 billion years after the big bang. “This kind of gas should still be cool and less abundant because these baby clusters are still accumulating and heating their gas,” says Zhou. This cluster, the only one of its kind spotted so far, looks far more grown-up than it ought to.

Its strange heat could be due to the presence of several particularly active galaxies among its members, including at least three that are pumping out enormous jets of energy. Those jets, and the frequent bursts of star formation, could heat up the gas far quicker than we previously suspected.

“What this really does is open a new window showing a phase of cluster evolution that we have never seen before,” says Zhou. He and his team are planning follow-up observations to hunt for more hot, young clusters like this one, in hopes of figuring out how unusual it really is.