As vast as the Milky Way may seem, our sprawling galaxy is but a speck next to galaxy clusters—collections of hundreds to thousands of galaxies bound together by gravity. At the heart of most clusters sit massive old galaxies, within which only a few new stars are born each year.
Now a multi-institution team led by MIT has identified a galaxy cluster seven billion light-years away that is among the most massive and most luminous in the universe. It’s known as SPT-CLJ2344-4243 or the Phoenix cluster, in honor of the constellation in which it resides.
While the cores of most galaxy clusters appear red, indicating that their stars are all very old, the Phoenix cluster’s core galaxy (shown in this artist’s rendering) is bright blue. This suggests that the surrounding gas is cooling rapidly, generating ideal conditions for star formation. Indeed, the galaxy churns out a dazzling 740 stars per year.
“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,” says Michael McDonald of MIT’s Kavli Institute for Astrophysics and Space Research. “But the central galaxy in this cluster has somehow come to life and is giving birth to prodigious numbers of new stars.”
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