Distant Quasar Sheds Light on Network of Filaments Connecting Cosmic Web

Astronomers have discovered a distant quasar illuminating a vast nebula of diffuse gas. The brilliant point sheds light on part of the network of filaments thought to connect galaxies in a cosmic web.

"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," said Sebastiano Cantalupo, one of the researchers, in a news release.

The standard cosmological model of structure formation in the universe predicts that galaxies are embedded in a cosmic web of matter, most of which is invisible dark matter. This web can be seen in results from computer simulations, but scientists have yet to see the actual filaments of diffuse, ionized gas--until now.

Now, researchers have detected the fluorescent glow of hydrogen gas resulting from its illumination by intense radiation from the quasar. The hydrogen gas emits ultraviolet light known as Lyman alpha radiation. The distance to the quasar is so great that the emitted light is "stretched" by the expansion of the universe from an invisible ultraviolet wavelength to a visible shade of violet by the time it reaches the Keck Telescope.

"We have studied other quasars this way without detecting such extended gas," said Cantalupo in a news release. "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 researchers found that the amount of gas in the nebula was at least ten times more than expected in computer simulations. The observations challenge their understanding of intergalactic gas and also give astronomers a new laboratory to test and refine their models. In addition, it reveals a bit more about the formation of galaxies in general, and allows scientists to learn more about the web that connects galaxies.

The findings are published in the journal Nature.