First direct observation of cosmic dark matter 'web' described

A hidden "web" of dark matter underlying the visible universe has been seen directly for the first time using a distant "cosmic flashlight," U.S scientists say. A distant quasar illuminating a vast nebula of diffuse gas has revealed part of the network of filaments thought to connect galaxies in a cosmic web, researchers at the University of California, Santa Cruz, say. The researchers used the 32-foot Keck I Telescope in Hawaii to detected a very large, luminous nebula of gas extending about 2 million light-years across intergalactic space, a university release said. "This 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," study first author Sebastiano Cantalupo said. "The light from the quasar is like a flashlight beam, and in this case we were lucky that the flashlight is pointing toward the nebula and making the gas glow, he said. The standard cosmological model of the structure of the universe predicts galaxies are embedded in a cosmic web of matter, about four-fifths of which is invisible dark matter. These filaments had never been seen until the Keck telescope detected the fluorescent glow of hydrogen gas resulting from its illumination by intense radiation from the quasar. "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," study co-author J. Xavier Prochaska, professor of astronomy and astrophysics at UC Santa Cruz, said.