Quasars, the Cosmic Web, and Dark Matter

Computer simulation of cosmic web illuminated by quasars

            Astronomers at the University of California, Santa Cruz have discovered evidence for the network of filaments theorized to connect galaxies. Using the Keck I Telescope at the W.M. Keck Observatory these astronomers have detected a very large very distant nebula that stretches about 2 million light years across. The nebula is twice as big as any previously detected nebula and is being illuminated by a very luminous quasar. This enormous nebula of diffuse gas is, for the first time, showing the structure of a portion of the network of filaments in the cosmic web. Current theory, along with computer simulation, predict that galaxies should form along this web of filaments that consist of mainly dark matter. The gravitational attraction of the dark matter should cause ordinary matter, such as the diffuse gas in the nebula, to follow the web pattern seen in computer simulations.  The nebula consists of mainly, if not all, hydrogen gas that is emitting ultraviolet light. It is the very luminous quasar that is exciting the hydrogen to emit Lyman alpha wavelength radiation. Because the quasar and nebula are so far away, the light it emits is being stretched so that the ultraviolet light, which cant be seen with naked eye, reaches the Earth as a visible violet color. The astronomers used a filter to observe the nebula at the visible wavelength seen at Earth. After analyzing the nebula they concluded that it contained ten times the amount of gas as predicted by computer models.  

http://www.sciencedaily.com/releases/2014/01/140119142452.htm