Deepest-Ever Field Image of Giant Galaxy Cluster Is a Brutal Reminder of Your Cosmic Insignificance

When it comes to deep space observations, our cosmological insignificance seems to grow with the resolution of our telescopes’ cameras. In the latest advance, astronomers constructed the deepest-ever images of Abell 3667, a massive galaxy cluster located 700 million light-years from Earth—and most of the tiny dots you see represent entire galaxies.

But the latest images of Abell 3667 also offer “whispering evidence of past galactic interactions,” which astronomers document in detail in a paper published today in The Astrophysical Journal Letters. The team, led by astronomers from Brown University, caught Abell 3677 at a particularly lustrous moment in space-time, during a merger of two of the clusters’ brightest galaxies. The stellar union, resembling a starry bridge stretching across the cluster, generated powerful gravitational bursts that yanked away the occasional stray star from other galaxies. 

Together, these lone stars emit a faint glow known as intracluster light (ICL)—and it’s this phenomenon that researchers are investigating to explore Abell 3677’s past. Specifically, it appears likely that Abell 3667 also formed from the rapid merger of two galaxy clusters, which previous X-ray and radio observations had predicted. This latest observation, however, represents the first ever optical evidence to support this idea.

“This is the first time a feature of this scale and size has been found in a local galaxy cluster,” Anthony Englert, study lead author, said in a statement. “We knew that it was possible for a bridge like this to form between two galaxies, but it hadn’t been documented anywhere before now. It was a huge surprise that we were able to image such a faint feature.”

The team had an unusually long observation period for this project, which partly enabled them to construct such a detailed image. In addition to the intracluster light, the researchers captured faint, wispy puffs of cosmic dust called integrated flux nebulae, seen as bluish ribbons of light streaking across the image.

“It was just a happy coincidence that so many people had imaged Abell 3667 over the years, and we were able to stack all of those observations together,” Englert noted.

The researchers have some outstanding questions about Abell 3677 and, more importantly, intracluster light. Fortunately, their timing couldn’t have been more impeccable; with the Rubin Telescope officially up and running, astronomers are now better equipped to further probe these questions. 

“Rubin is going to be able to image ICL in much the same way as we did here, but it’s going to do it for every single local galaxy cluster in the southern sky,” Englert said. “What we did is just a small sliver of what Rubin is going to be able to do. It’s really going to blow the study of the ICL wide open.”

Essentially, if this new image doesn’t make you feel small, you might want to wait for the soon-to-come Rubin versions of this image. In fact, if Englert is right, we’ll be seeing multiple versions of this image, and in higher resolution, too. So, for better or worse, we humans will only get smaller from here.