Like an ethereal cosmic spider web, filaments of gas form a complex, interconnected structure that links galaxies to one another. But, just as whisper-thin threads of spider silk can be nearly invisible, this cosmic web is faint and difficult to detect. Now astronomers have made the first detailed picture of light emitted by the gas. The newly revealed filaments extend for millions of light-years, researchers report in the Oct. 4 Science.

Computer simulations predicted the existence of the cosmic web, and astronomers previously have caught glimpses of a single filament (SN: 1/20/14). But scientists hadn’t seen the network stretching between multiple galaxies until now. “Finally, we actually have a picture,” says astrophysicist Michele Fumagalli of Durham University in England.

Fumagalli and colleagues studied a region of the sky that contains a protocluster of galaxies — a region where a large cohort of galaxies is beginning to assemble. Galaxies within the cluster emit ultraviolet light, a result of new stars forming inside or of churning regions around supermassive black holes at the galaxies’ centers. The filaments of gas absorb that light and reemit it. Using the European Southern Observatory’s Very Large Telescope in Chile, the astronomers detected the reemitted light.

After the Big Bang 13.8 billion years ago, scientists believe that gravity caused matter to collapse into sheets and filaments. In regions where the matter was especially dense, galaxies formed, feeding on gas from the cosmic web. The new picture of the filaments supports this origin story.