A distant galaxy seems to be the only one left in its cluster. It has all the signatures of a galaxy cluster that should contain hundreds of galaxies, but it appears to be all alone, which may cause a rethink of how galaxy clusters form and evolve.
at the University of Texas Rio Grande Valley and his colleagues examined the 3C 297 galaxy, which is about 9.2 billion light years from Earth, using three powerful telescopes. They found that it contained a supermassive black hole spewing out a colossal jet of matter, but the jet is bent and creating a burst of X-rays, indicating that it is interacting with the galaxy’s surroundings. They also found that the galaxy is surrounded by glowing gas with temperatures of tens of millions of degrees, a hallmark of galaxy clusters.
What they didn’t find was any other galaxies in the area. “This galaxy is very powerful, has a powerful jet and has no companions whatsoever,” says Madrid. “So the question is, how did this galaxy become so big and so powerful without being part of a galaxy cluster? It’s powerful but lonely.”
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For 3C 297 to have such a powerful jet, the galaxy must have assimilated some neighbouring galaxies. “For a galaxy to have this big jet, you need to feed the black hole,” says Madrid. “For breakfast they have a galaxy and for lunch they have another galaxy,” he says. The lack of other nearby galaxies hints that it may have swallowed up all of the other galaxies in its cluster, which explains how a single galaxy could have all the accoutrements of an entire cluster.
If that is what happened, it would make this a structure called a fossil group, not an active cluster anymore. While we have detected fossil groups before, none have been as distant as this one.
That could potentially be a problem for theories on how fast galaxies and galaxy clusters can form, because the huge distance to 3C 297 means that the cluster had formed and been devoured within the 4.6 billion years after the big bang. “If the galaxy ate all its neighbours, it did that very fast by astronomical standards – it takes a long time to eat a galaxy,” says Madrid. “So this is an extreme example of how these powerful galaxies can come to be, and those extreme examples are the ones that push the limits of our theories and our understanding.”
The Astrophysical Journal
