Astronomers find for the first time 'glue' that links galaxies together in a cosmic web

01/21/2014 - 00:00

The standard cosmological model of structure development in the universe envisions that galaxies are nested in a cosmic web of matter.

Astronomers from the University of California – Santa Cruz have found a far-off quasar lighting up a very large nebula of spread out gas, showing for the first time part of the network of filaments believed to link galaxies in a cosmic web.

Utilizing the 10-meter Keck I Telescope, the researchers spotted an extremely large, bright nebula of gas spreading approximately 2 million light-years across intergalactic space.

“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,” posited first author Sebastiano Cantalupo, a postdoctoral fellow at UC Santa Cruz, in a statement.

The standard cosmological model of structure development in the universe envisions that galaxies are nested in a cosmic web of matter. The web is observed in the findings from computer simulations of the development of structure in the universe, which reveal the dispersion of dark matter on large scales, including the dark matter halos in which galaxies develop and the cosmic web of filaments that link them. Gravity forces ordinary matter to follow the dispersion of dark matter, so filaments of spread out, ionized gas are believed to trace a pattern akin to that observed in dark matter simulations.

Prior to this research, these filaments have never been observed. Intergalactic gas has been identified by its absorption of light from bright background sources, but those findings don’t show how the gas is dispersed. In this study, astronomers identified the fluorescent glow of hydrogen gas due to 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,” explained coauthor J. Xavier Prochaska, professor of astronomy and astrophysics at UC Santa Cruz.

The hydrogen gas brightened by the quasar gives off ultraviolet light called Lyman alpha radiation. The distance to the quasar — approximately 10 billion light-years — is so great that the discharged light is “stretched” by the expansion of the universe from an invisible ultraviolet wavelength to a visible shade of violet by the time it’s detected by the Keck Telescope. The astronomers determined the wavelength for Lyman alpha radiation from the distance to the quasar and constructed a special filter for the telescope’s spectrometer to obtain an image at that wavelength.

“We have studied other quasars this way without detecting such extended gas,” Cantalupo noted. “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. We think this is part of a filament that may be even more extended than this, but we only see the part of the filament that is illuminated by the beamed emission from the quasar.”

The study’s findings were published in the journal Nature.