Researchers may have spotted the "cosmic web" that connects galaxies to one another.
The team observed a "distant quasar illuminating a vast nebula of diffuse gas," it is believed to belong to a greater network of threads that connect the universe together, a University of California-Santa Cruz news release reported.
A quasar is a "active galactic nucleus" that gives off intense radiation, the source of which is a black hole at the center of the host galaxy.
The nebula they picked up is about two million light-years long and sits in 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," first author Sebastiano Cantalupo, a postdoctoral fellow at UC Santa Cruz, said.
The proposed "cosmic web" is believed to be made up of about 84 percent dark matter, which may be why the phenomenon has remained so elusive. This is the first time researchers have seen evidence of the intergalactic threads.
Until now researchers had only observed these threads in computer models that simulated the "evolution of structure in the universe." The model showed "dark matter halos" where galaxies are born and the intertwined web that connects them.
"Gravity causes ordinary matter to follow the distribution of dark matter, so filaments of diffuse, ionized gas are expected to trace a pattern similar to that seen in dark matter simulations," the news release reported.
In the past researchers have observed intergalactic gas that had absorbed light from a nearby object, but this was not enough to contribute to the understanding of how this gas is distributed. In this new observation the scientists were able to view the "fluorescent glow of hydrogen gas" thanks to radiation from the bright 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," coauthor J. Xavier Prochaska, professor of astronomy and astrophysics at UC Santa Cruz, said in the news release.
The quasar gives off light called Lyman alpha radiation. The object is about 10 billion light-years away, so by the time the light reached the researchers' Keck I Telescope it was "stretched."
"We have studied other quasars this way without detecting such extended gas," 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. 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."
Researchers had also detected "dark galaxies" using the same tools.
"The dark galaxies are much denser and smaller parts of the cosmic web. In this new image, we also see dark galaxies, in addition to the much more diffuse and extended nebula," Cantalupo said. "Some of this gas will fall into galaxies, but most of it will remain diffuse and never form stars."
This new observation showed the gas within the nebula was about 10 times more than had been predicted in the the computer simulation.
"We think there may be more gas contained in small dense clumps within the cosmic web than is seen in our models. These observations are challenging our understanding of intergalactic gas and giving us a new laboratory to test and refine our models," Cantalupo said.
