Galaxy cluster SpARCS1049 is out there forming 900 some odd stars per year out of the gas and dust between galaxies. This is not normal. I actually studied galaxy clusters as a grad student, and normal massive clusters are filled with extremely hot gas that can’t form stars because the atoms are moving too fast to consider collapsing into stars. This gas is generally heated by jets from a central supermassive black hole that is active in the central galaxy, a cD galaxy that marks the cluster center. This supermassive black hole is active because it is feeding on material driven into its core through interactions with other systems, many of which it’s consuming. 

In SpARCS1049, it doesn’t so much have a central cD galaxy as it has an off-center could-have-been-a-cD galaxy, and that galaxy isn’t active and isn’t heating all the gas in the intergalactic spaces in this cluster. Thus, that gas has a chance to cool, collapse, and form stars in a very not-normal way. It’s as if the universe said, let’s move this galaxy over and see what happens. The result was stars. Lots and lots of stars. 

The team behind this work, which appears in the Astrophysical Journal Letters under the first author, Julie Hlavacek-Larrondo, theorizes that this kind of a system may have been common in the early universe when clusters were still settling into their final shapes and may have been responsible for forming a lot of the universe’s early stars. 

More Information

Chandra X-ray Observatory press release 

“Evidence of Runaway Gas Cooling in the Absence of Supermassive Black Hole Feedback at the Epoch of Cluster Formation,” J. Hlavacek-Larrondo et al., 2020, Astrophysical Journal Letters (Preprint on arxiv.org)