Scientists have used a quasar to illuminate a 1.5 million light year stretch of a "cosmic web" filament. Picture: S Cantalupo. SCIENTISTS say they have recorded the first glimpse of the "cosmic web," a colossal network of giant intersecting threads which holds the universe together. Astronomers have speculated for years that gigantic voids in the universe are crisscrossed by "filaments" of dark matter. These filaments siphon together gases and other material, forming galaxies along their length and tightly packed clusters of galaxies at their junctions. However, dark matter emits little if any radiation, including light. Consequently, the threads of the cosmic web have only been observed in computer simulations. US and German scientists say they have now set eyes on a cosmic web filament, after they used a quasar - a disk of gas and stars around a supermassive black hole - as a "flashlight." "Bright quasars can "illuminate" the densest knots in the surrounding cosmic web," the team explains today in the journal Nature. The researchers used the light of the quasar, known as "UM 287," to boost the visibility of a stream of hydrogen gas stretching far along the filament into intergalactic space. Apart from short-lived explosive bursts, quasars are considered the brightest objects in the universe. The team used a custom-built filter on the Very Large Telescope, a network of observatories on a plateau in northern Chile, to observe the hydrogen stream which is about 1.5 million light years long. Scientists have hunted evidence of the cosmic web since the term was coined in the 1990s. In 2009, astronomers from the European Southern Observatory claimed their discovery of a massive assembly of galaxies - located almost seven billion light-years away - as "solid proof" of the web in the distant universe. "These filaments are millions of light years long and constitute the skeleton of the universe," the ESO reported. In 2012, astronomers using telescope data from Mauna Kea in Hawaii announced they had detected a bridge of dark matter connecting two distant galaxy clusters known as Abell 222 and Abell 223. Rather than observing the bridge directly, they inferred it from distortions in light passing through from more distant galaxies.