The grand "cosmic web" is a picture that has fascinated us since the beautiful Millennium Simulation was run in 2005, showing us a Universe full of matter often clumped together but intricately bound by thin filaments. For the first time, these thin filaments of gas have been directly seen using one of the largest telescopes on Earth.
PHOTOS: Cosmic Hotshots from Keck Observatory
Clouds of gas, by their nature, are diffuse and difficult to detect. Often, we can see gas that lies along a line of sight to distant bright object, such as a quasar. However, that only gives insight into one small piece of that cloud.
A quasar is the bright central region of a galaxy that is being powered by a supermassive black hole that is gobbling up surrounding material. A team of astronomers, with lead author Sebastiano Cantalupo, looked towards such a quasar 10 billion light years away and found it illuminating a gas cloud far too large to be part of a galaxy cluster.
This gas resides in the intergalactic medium, the spaces between galaxies. It is two million light years across, a distance equal to roughly the distance between the Milky Way Galaxy and the Andromeda Galaxy. It was detected in the faint glow given off by hydrogen atoms that were excited by the radiation of the nearby quasar using the 10-meter Keck I telescope in Hawaii.