Celestial filaments link together galaxy clusters into cosmic webS

Large groups of galaxies come together to form clusters, and those clusters are linked together by vast streams of hot gas known as filaments. These intergalactic links reach temperatures well over a million degrees and are almost completely invisible...until now.

Filaments represent the universe at its most unimaginably vast and cosmic scale. Filaments link together clusters of galaxies into superclusters, and in turn even larger filaments link together these superclusters into a continuous web that represents the only relief from the endless void of empty space. The average filament can be well over 100 million light-years long.

At that sort of size, you'd really think filaments would be hard to miss, but they're surprisingly tricky even to observe. Superclusters themselves are evidence of where matter clumped together in the expansion right after the Big Bang, and filaments are collections of all the leftover gas that didn't make it into the superclusters.

While the superclusters cooled down considerably in temperature, the gas in the filaments remain spectacularly hot, reaching temperatures of a million degrees Celsius. They mostly emit X-rays, meaning that's the best light in which to see them. But superclusters give off a lot more X-ray light, almost completely overwhelming our ability to observe the filaments.

Celestial filaments link together galaxy clusters into cosmic webS

Astronomers recently caught a break with the discovery of a galaxy inside the filament linking together the galaxy clusters Abell 1763 and Abell 1770. The galaxy in question has a weird boomerang shape and emits very unusual ratio of radio to infrared light. Both of these are the result of the galaxy's passage through the hot gas of the filament, which is reshaping and reworking the galaxy's chemistry as it move s through.

Chief researcher Louise Edwards of the California Institute of Technology explains the importance of the filaments:

"These filaments are integral to the evolution of galaxy clusters — among the biggest gravitationally bound objects in the universe — as well as the creation of new generations of stars."

These new observations have allowed astronomers to both confirm early theories about filaments and learn entirely new information. Most amazingly, they were able to figure out the density of the region inside the filament by measuring the pressure the filament's particles exerted on the galaxy. They determined the filament has a density that is 100 times greater than the universal average, which is even more incredible when you consider the immense size of the filament. That's a whole lot of hot matter crammed into the spaces between galaxies.

[The Astrophysical Journal]