In a research paper published in Nature this Sunday, the astronomers describe how they took the image using the 10-meter telescope at the W. M. Keck Observatory in Hawaii:
This deep image (on the left, above) shows the nebula (cyan) extending across 2 million light-years that was discovered around the bright quasar UM287 (at the center of the image). The energetic radiation of the quasar makes the surrounding intergalactic gas glow, revealing the morphology and physical properties of a cosmic web filament.
According to lead study author Sebastiano Cantalupo, the 2-million-light-year Cosmic Web filament "is a very exceptional object: it's huge, at least twice as large as any nebula detected before, and it extends well beyond the galactic environment of the quasar."
The image confirms the theory of Cosmic Web that entangles the Universe itself, a network of threads that is made mostly—about 84 percent—of invisible dark matter:
Computer simulations (on the right, above) suggest that matter in the universe is distributed in a "cosmic web" of filaments, as seen in the image above from a large-scale dark-matter simulation (Bolshoi simulation, by Anatoly Klypin and Joel Primack). The inset is a zoomed-in, high-resolution image of a smaller part of the cosmic web, 10 million light-years across, from a simulation that includes gas as well as dark matter (credit: S. Cantalupo).
The image taken by Cantalupo et al was possible because of the intense radiation of the quasar UM287 which "like a flashlight, [can] illuminate part of the surrounding cosmic web and make a filament of gas glow."
This is the first time in history that one of these filaments has been observed, says UC Santa Cruz professor of astronomy and astrophysics J. Xavier Prochaska:
This quasar is illuminating diffuse gas on scales well beyond any we've seen before, giving us the first picture of extended gas between galaxies. It provides a terrific insight into the overall structure of our universe.
There's also an object called dark galaxies. Describing the unique image, Cantalupo says that "the dark galaxies are much denser and smaller parts of the cosmic web. In this new image, we also see dark galaxies, in addition to the much more diffuse and extended nebula. Some of this gas will fall into galaxies, but most of it will remain diffuse and never form stars."