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largescalestructure
Dark Matter and Galaxy Formation
The Electronic Universe (University of Oregon)
Video: 1001 kB, MPEG
For every gram of matter in the universe that shines or radiates energy, there are between 10 and 100 grams of matter that give off no light at all. This mysterious dark matter
is not made up of atoms or molecules, so scientists can only theorize and speculate about its nature. However, the gravitational effects of dark matter are indisputable and affects the motion and evolution of the largest structures in the universe, including galaxies, clusters, and superclusters. This movie shows how dark matter moves and distributes itself to make certain types of galaxies.
Dark matter and structure development
There is a wide range of galaxy types, shapes and sizes, which means the process of forming galaxies is very complex. In addition, most all galaxies today are embedded in some larger-scale structure. Structure formation could have occurred either from the fragmentation of very large regions into smaller regions, or from the gravitational attraction of small pieces into successively larger structures. Both formation scenarios lead to a highly clustered universe with structure on many different size scales. This particular movie shows how an evenly distributed amount of dark matter, given time, will form structures such as elliptical blobs, webs, and filaments, purely from the force of gravity.
Austin Reiter
The Cosmic Mircowave Background
Richard McCray (JILA, University of Colorado)
Video: 1 MB, MPEG
The best scientific model of our cosmic origin is known as the Big Bang. According to this model, the universe was incredibly hot—billions of degrees in every direction—a few minutes after the universe first began to expand. After about half a million years, the cosmos cooled enough for matter and energy to separate, creating the cosmic microwave background radiation (CMBR). All of the large-scale structure in the universe began from fluctuations in the temperature in the CMBR. In the 1990's, astronomers used the Cosmic Background Explorer Satellite (COBE) to show that the CMBR was almost, but not quite, perfectly smooth (smooth to one part in a hundred thousand). This is akin to a sheet of glass the size of a football field with bumps only as big as grains of sand.
The cosmic web
According to astronomical theories, these tiny variations in the CMBR are manifestations of very slight fluctuations in the density of matter in the early universe. Over billions of years, gravity attracts the matter toward regions of slightly elevated density, and this process becomes amplified as these regions become more dense. Astronomers call this process gravitational instability and suspect that this process will amplify the barely-perceptible fluctuations that we see in the early universe into the giant structures (voids and superclusters) that we see in the universe today. In this movie, we fly around and through a cube of space many millions of light-years across. The web-like structures in this space trace the distribution of matter; the intersection points of the web are the locations of galaxies, clusters, and superclusters—the densest concentrations of matter in the universe.
Austin Reiter
Formation of X-Ray Clusters
Greg L. Bryan and Michael L. Norman (NCSA)
Video: 121 kB, MPEG
Using X-ray telescopes in Earth orbit, astronomers have discovered that rich clusters of galaxies are immersed in halos of super-hot, million-degree gas. This hot gas is a byproduct of the galaxy formation process and emits large amounts of energy in the form of X-rays. Many of these X-ray clusters
are so luminous that they can be seen from many billions of light-years away. By studying the size and distribution of X-ray clusters, astronomers are mapping the large-scale structure of the universe.
Watching clusters form
In this movie, the white square represents the region over which the calculations were performed. Outside the square, the pattern is repeated. Each side of the square is 300 million light-years across (1 light-year equals 6 trillion miles). The calculation begins about one billion years after the Big Bang, when the Universe was more dense and uniform compared to today's Universe. Over time, matter becomes distributed in clusters and clumps, leaving other regions relatively empty. X-ray clusters will form where the largest clumps of matter form; astronomers call the empty regions voids.
Austin Reiter
