The discovery of the most distant galaxy cluster, SPT-CL J2215-3537 (SPT2215 for short), is providing astronomers with some much-needed insight into how these gigantic structures formed and why the universe looks like it does today. This is due to the fact that this cluster is located 8.4 billion light-years away and is unusually young, meaning it has been untouched by violent collisions with other clusters of galaxies as it has grown.
While galaxy clusters are some of the largest structures in the universe, their growth and formation is still largely a mystery. In order to understand how these clusters form, astronomers need to study clusters at different ages and distances. To that end, scientists have been looking for clusters that are far away and still in an “unspoiled” or “relaxed” state, meaning they have not been disturbed by violent collisions with other clusters or groups of galaxies as they increase in size.
What makes SPT2215 so special is that it is an unusually young galaxy cluster located 8.4 billion light-years away from Earth. This means it is seen when the universe was only 5.3 billion years old, compared to its current age of 13.8 billion years. Until this discovery, astronomers had not found a relaxed galaxy cluster this far away. In fact, scientists were not sure they would find a galaxy cluster that was relaxed at this age of the universe, because they are usually still undergoing the turmoil of mergers with other clusters or groups of galaxies as they increase in size.
Now that SPT2215 has been identified, astronomers have been able to gain more insight into how these giant structures form and why the universe looks like it does today. By studying this distant and relatively undisturbed cluster, astronomers can begin to piece together a story as to how these massive structures grow and change over time.
Another interesting aspect of SPT2215 is the evidence for large amounts of star formation happening in its center, but the real surprise is what’s happening around the black hole – a prodigious amount of star formation. This unexpected burst of star formation has raised more questions than answers for astronomers. How does a supermassive black hole, an object that emits intense radiation, allow for so much star formation? And what does this tell us about the evolution of galaxies in the universe?
To investigate these questions, astronomers have conducted extensive studies on SPT2215. Three papers have been published on the cluster in the past few years; the most recent, led by Michael Calzadilla and his colleagues, was published in April 2023 in The Astrophysical Journal. The findings from Calzadilla’s paper and other research suggest that SPT2215’s black hole has cooled enough that it isn’t emitting enough radiation to prevent star formation from taking place in its vicinity. This would explain why there is so much activity around it.
The cluster is also notable for its isolated environment. There are no other galaxies within 600,000 light-years that are as bright or extended as SPT2215, suggesting that it hasn’t experienced a merger with another cluster in at least a billion years. This provides evidence that SPT2215 is a “relaxed” system – one that is relatively unaffected by cosmic forces such as merging galaxies or intense radiation from nearby objects.This newfound evidence for star formation around a supermassive black hole brings us one step closer to understanding how these objects influence their surroundings over long periods of time. With further research, we may be able to gain insight into how galaxies evolve and better understand the mysterious workings of the universe.