Thanks to the combined power of the Atacama Large Millimeter/submillimeter Array (ALMA) and JWST, researchers could see the complex interactions happening within the famous multi-galaxy collision event known as Stephan’s quintet. The ensemble has four galaxies actively interacting (the fifth galaxy is just nearby) and the intergalactic medium around them is experiencing some violent activities.

One of the galaxies, NGC 7318b, is coming into the group at a really high speed of 800 kilometers (500 miles) per second, going through a stream of gas likely left there by a much older interaction between other galaxies in the group. As the galaxy crossed this stream, it created an enormous shockwave several times larger than the Milky Way (which is 105,000 light-years across) – and that shock is creating some really weird stuff.

“As the shockwave passes through this clumpy streamer, it is creating a highly turbulent, or unsteady, cooling layer, and it’s in the regions affected by this violent activity that we’re seeing unexpected structures and the recycling of molecular hydrogen gas. This is important because molecular hydrogen forms the raw material that may ultimately form stars, so understanding its fate will tell us more about the evolution of Stephan’s Quintet and galaxies in general,” lead investigator Philip Appleton, from Caltech’s Infrared Processing and Analysis Center (IPAC), said in a statement.

That’s not the only peculiar thing that has been spotted. The team saw a large cloud of cold gas being broken apart and stretched into a long tail of warm hydrogen, before being recycled between hot and cold phases. Or two cold gas clouds connected by a bridge of hot gas. Or a cold gas cloud creating a ring in a filament, like a high-speed bullet. To explain what is happening, the team is still waiting for more data.

“A molecular cloud piercing through intergalactic gas, and leaving havoc in its wake, may be rare and not yet fully understood,” added Bjorn Emonts, an astronomer at NRAO and a co-investigator on the project. “But our data show that we have taken the next step in understanding the shocking behavior and turbulent life-cycle of molecular gas clouds in Stephan’s Quintet.”

If all these space oddities were not enough, the team is also seeing large cold dense clouds collapse under the shocks and forming new stars. This is expected in these merging events and is pretty much the formation of a dwarf galaxy. Across this galaxy group, there is a lot of cold gas but despite the abundance, there are fewer stars forming than expected. A very peculiar affair.

“The shock wave in the intergalactic medium of Stephan’s Quintet has formed as much cold molecular gas as we have in our own Milky Way, and yet, it forms stars at a much slower rate than expected. Understanding why this material is sterile is a real challenge for theorists. Additional work is needed to understand the role of high levels of turbulence and efficient mixing between the cold and hot gas,” added co-investigator Pierre Guillard, a researcher at the Institut d’Astrophysique de Paris.

Follow-up observations will collect spectroscopic data on the gas which will allow tracing of the motion of the gas as well as the precise temperature. 

The observations were presented at the 241st meeting of the American Astronomical Society (AAS) in Seattle, Washington.