A new galaxy cluster has been discovered that is one of the biggest and brightest in our universe, and has an exceptional bright blue core.
Officially known as SPT-CLJ2344-4243, it is 7 billion light-years away, and has been dubbed the Phoenix cluster after the constellation where it is located.
Most galaxy clusters have red cores, because the stars they contain are old. This cluster’s blue core suggests the gas around it is cooling rapidly.
A team of researchers led by the Massachusetts Institute of Technology (MIT) have studied the Phoenix cluster closely after it was detected with the South Pole Telescope.
“Central galaxies have typically been referred to as ‘red and dead’—just a bunch of old stars orbiting a massive black hole, and there’s nothing new happening,” explained research leader Michael McDonald at MIT’s Kavli Institute for Astrophysics and Space Research in a press release.
“But the central galaxy in this cluster has somehow come to life, and is giving birth to prodigious numbers of new stars.”
Based on popular theory, the gas at a cluster’s core should cool over time, creating a cold flow that would condense into new stars. But no clusters have been observed to cool at predicted rates.
“What’s interesting about the Phoenix cluster is that we see almost all the cooling that was predicted,” McDonald said. “It could be that this is earlier in the evolution where there’s nothing stopping it, so it cools and becomes a starburst … in fact, there are few things forming stars in the universe faster than this galaxy.”
The team imaged the cluster with 10 different space and ground-based telescopes at various wavelengths to get a complete view of its features.
“The central black hole is very bright in the X-ray, but the star formation is very bright in the optical and ultraviolet,” McDonald said.
The researchers calculated its mass and luminosity, and then investigated star formation, finding it generates 740 new stars per year, probably due to rapid cooling.
McDonald hopes to continue studying the Phoenix cluster using the Hubble Space Telescope. “You’d see these fantastic blue filaments where stars are forming out of cooling streams,” he said. “It should look quite remarkable, instead of our ground-based images which show a blob of blue light.”
However, the extreme cooling observed might not be as unusual as it seems.
“It could be a timing thing, where one percent of the time you get this vigorous star formation and runaway cooling,” McDonald concluded. “It might be that every cluster we see goes through this phase, but it’s so short-lived that this is the only one we’ve found. And we were in the right place at the right time.”
The study will be published in Nature on Aug. 16.
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