Astronomers get their first good look at the cosmic web that connects galaxies

The web extends over millions of light-years.

This movie shows a galaxy cluster from the C-EAGLE simulation, providing a view of a region comparable to the one where the filaments have been detected. The color map represents the same emission from the gas filaments as the one detected in observations,. At the convergence of these filaments, a massive cluster of galaxies are assembling.

Galaxies that are spread out in the vastness of the universe are actually connected.

A mysterious, dark web feeds their star formation and helps them grow, and until recently, scientists have only been able to build models of this faint cloud of gas. But new research has found something cosmic: Astronomers have now witnessed this galaxy web in unprecedented detail.

Gas filaments are one of the largest structures of the universe, if not the largest, and they extend across millions of light-years in a web-like formation. They are also extremely faint, making it difficult to detect them in the voids between galaxies.

But researchers report they have found evidence for multiple filaments that spread out across over three million lightyears, connecting an entire cluster of galaxies. Their work is compiled in a paper, published in the journal Science on Thursday.

Hideki Umehata, PhD., a researcher at the RIKEN Cluster for Pioneering Research and the University of Tokyo, and lead author of the study, says there have been numerous attempts to observe these filaments but there has not been a successful detection thus far.

“We focused on the relatively bright part of the cosmic web,” Umehata tells Inverse. “And we finally found the filament structure.”

This map shows the gas filaments (blue) that run from the top to the bottom of the image, detected using the MUSE instrument at the Very Large Telescope. The white dots embedded within these filaments are very active star forming galaxies which are being fed by the filaments, and which are detected using the Atacama Large Millimeter/submillimeter array.
This map shows the gas filaments (blue) that run from the top to the bottom of the image, detected using the MUSE instrument at the Very Large Telescope. The white dots embedded within these filaments are very active star forming galaxies which are being fed by the filaments, and which are detected using the Atacama Large Millimeter/submillimeter array.

Thank you, supermassive black hole

The reason why that particular region of the sky is bright is because it hosts a number of supermassive black holes, and very active galaxies with lots of star formation activity, which in turn illuminates the gas filaments and makes them easier to detect.

These findings support the longstanding model for galaxy formation, and how these threads of gas, composed mostly of hydrogen, are essentially the building blocks for galaxies.

Erika Hamden, an astrophysicist at the University of Arizona, who was not involved in the study, explains how the gas filaments aid star formation.

“The filaments are a fuel reservoir for the galaxies,” Hamden tells Inverse. “The galaxies have hydrogen inside of them and use that hydrogen to create stars…it helps keep star formation happening in the galaxies, and slowly the galaxy gets bigger.”

Why this study is so exciting

“It’s exciting because it’s a confirmation of our model of the universe that these filaments exist,” Hamden says.

Previous measurements of the gas filaments have been made before, but this full view of the vast extent of the cosmic web, and with this level of detail, has never been successfully done.

“This kind of gas filament has been predicted for years, but this is the first time we see the gas filament connecting a number of galaxies, and finally validate our [models of the] assembly of galaxies,” Umehata says

The team behind the latest findings are planning future observations of the filaments in order to capture the growth of the galaxies, as they feed off of the threads of gas, and find out how common these filaments are across larger areas of the universe.

“We still see a tiny window of the sky area,” Umehata says. “We would like to enlarge our window and see a more comprehensive view of the cosmic web, and the evolution of the cosmic web structure across the universe.”

The process of star formation and expansion of galaxies is quite slow, explains Hamden, and therefore hard to comprehend. “But these detections that are starting to be made, like this one in this paper, actually observe the process,” Hamden says.

“We’re at the tip of the iceberg,” she adds.

Media via Hidek Umehata, Joshua Borrow using C-EAGLE