The vast and mysterious great Cosmic Web is composed of dark matter--whose identity we do not know. However, scientists strongly suspect that the dark matter is composed of exotic non-atomic particles that do not interact with light--which is why the Cosmic Web is transparent and invisible. In January 2014, astronomers announced that they have spotted a remote quasar lighting up an enormous nebula of gas, revealing for the first time the web-like network of transparent filaments believed to connect the starlit galaxies embedded in the Cosmic Web. Like sparkling dewdrops suspended on the web of an enormous spider, this arrangement of galaxies traces the large-scale structure of the Universe. dark web
A team of astronomers at the University of California, Santa Cruz, led the study, published in the January 19, 2014 issue of the journal Nature. Using the 10-meter Keck I Telescope Observatory poised atop the Mauna Kea volcano in Hawaii, the team of scientists spotted an enormous, brightly shining nebula composed of gas that extends 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," explained Dr. Sebastiano Cantalupo, the lead author of the study. Dr. Cantalupo is a postdoctoral fellow at UC Santa Cruz.
Quasars are exceptionally brilliant objects that are often observed inhabiting the ancient and very remote Universe. These extraordinarily distant bodies are thought to have first caught fire a "mere" few hundred million years after the inflationary Big Bang birth of the Universe almost 14 billion years ago. Quasars dazzle the Cosmos with their fierce, brilliant fires--they are actually the accretion disks encircling young, voracious, and greedy supermassive black holes lurking in the hearts of baby galaxies that were forming in the very early Universe. Supermassive black holes haunt the dark hearts of almost all--if not all--large galaxies, and they weigh-in at millions to billions of times more than our Star, the Sun. Our own large, barred-spiral Galaxy, the Milky Way, holds a supermassive black hole in its secretive heart. It is called Sagittarius A* (Sgr A*, for short), and it is relatively light-weight, by supermassive black hole standards, weighing merely millions--as opposed to billions--of times more than our Star.
The team of astronomers, led by Dr. Cantalupo, used an extremely bright quasar, seen as it appeared when the Universe was "only" about 3 billion years old, to light up the dim gas floating around in this brilliant celestial object's general neighborhood. The rushing sea of light flowing out from the quasar causes hydrogen atoms in the gas to send forth a tattle-tale wavelength of ultraviolet radiation.
As the Universe continues in its relentless expansion, this radiation is stretched to ever longer wavelengths, ultimately becoming visible light. Dr. Cantalupo, Dr. J. Xavier Prochaska, and their team at UC Santa Cruz, studied that gushing, brilliant, ancient light, with Keck I. The images derived from Keck reveal a cloud of gas that is more than 10 times the diameter of our Galaxy! This represents the very first discovery of radiation flowing from a cloud "on scales far beyond a Galaxy", Dr. Prochaska said in the January 19, 2014 Nature News.
The Standard Cosmological Model of structure formation in the Universe predicts that galaxies are embedded in the filaments of the great Cosmic Web, most of which (about 84%) is composed of the mysterious, transparent, ghostly dark matter. This Cosmic spider's web is observed in computer simulations that strive to model the evolution of structure in the Universe. The simulations show the evolution of the dark matter on large scales, including the dark matter halos in which galaxies are born and the Cosmic Web composed of dark matter filaments that connect them.
The force of gravity causes "ordinary" atomic matter to follow the distribution of the dark matter. In this way, filaments of diffuse ionized gas are believed to outline a spidery pattern like the one seen in dark matter computer simulations.
A Cosmic Spider's Web
At the instant of our Universe's inflationary Big Bang birth, almost 14 billion years ago, there was a tremendous blast of brilliant light. Particles of light, called photons, of very high-energy electromagnetic radiation flew out from extremely searing-hot matter composing the primordial Cosmos. In the primordial Universe, however, light was unable to blast its way through the Cosmos freely. This is because, at the extraordinarily high temperatures of the very ancient Universe, matter was ionized. Hence, any atoms that managed to congeal in this hot environment were speedily ripped to shreds. The reason for this is that positively charged atomic nuclei could not keep a grip on their encircling clouds of negatively charged electrons. Electrically charged particles constantly emit and absorb photons. For the first 400,000 years of our Universe's existence, light was being constantly emitted, then absorbed, then emitted, and then absorbed again--and again! This cycle continued for a much longer period of time than human civilization has flourished on Earth! This ancient confusion continued for hundreds of thousands of years--until the extraordinarily high temperatures of the primordial Universe at last fell to less than five thousand degrees Fahrenheit.
All of the billions upon billions of starlit galaxies that blasted the early Universe with light appear to swarm around the perimeters of enormous cavities that can be as much as 150 light-years across. These great Voids are black because they are almost--but not entirely--empty.
These enormous great Cosmic Voids compose about 50% of the volume of the entire Cosmos. On large-scales, the Universe looks frothy, with heavy filaments of dark matter twisting themselves around each other to form the Cosmic Web. These transparent filaments are lit by the brilliant fires of vast sheets of intertwining galaxies. Enormous black Voids, which interrupt this transparent, intertwining, mysterious spidery structure, outlined by the sparkling flames of stars, are almost entirely devoid of galaxies. The Voids contain only a relatively small number of galaxies--which makes them appear to be empty when compared to the star-blasted Cosmic Web, that braids itself around them into a complex and convoluted structure.
Wherever we look in our vast Cosmos, we observe this same strange spidery pattern. Starlit, fiery galaxies are observed to be swarming around the perimeters of immense, black, almost empty Voids. This complex, twisted Web is richly endowed with matter, of both the so-called "ordinary" atomic kind, and the exotic and bizarre non-atomic dark kind.
If we were able to observe the Universe the way it really is, with our Earth-evolved human eyes, we would understand that most of the matter in it is exotic and non-atomic. The starlit galaxies and immense clusters of galaxies are embedded in halos of this mysterious, non-atomic, and invisible dark matter. The transparent dark matter weaves the heavy filaments of the Cosmic Web throughout the vastness of Space and Time.
