How is matter distributed in the universe? Is it distributed randomly, or does it form some type of pattern in 3-dimensions? When the astronomers Margaret Geller, John Huchra, and Valerie de Lapparent sought to answer this question in the 1980s by observing thousands of galaxies, they discovered that galaxies clustered to form extended structures reminiscent of soap bubbles, with voids separating the clusters. The Sloan Digital Sky Survey (SDSS) has observed a million galaxies—extending the work of these three astronomers—a small fraction (17,193) of which can be manipulated below with your mouse. (The Las Campanas Redshift Survey, and 2dF Galaxy Redshift Survey also observed thousands of galaxies.)

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3D Plot of SDSS Galaxies

Because light from other galaxies is blocked by gas and dust in our Milky Way galaxy, astronomers can observe only above and below our galactic disk, with earth at the point where the two fan-shaped wedges meet. Light observed from the most distant galaxies, the edges of the “fan,” was emitted 276 million years ago.

By taking a thin slice of the galaxy distribution (31,966 galaxies)—where light from the farthest galaxy was emitted 1.2 billion years ago—the observed galaxy distribution (below left) can be more easily compared to the same number of randomly distributed galaxies (below right), and there is certainly no similarity. The red image is a crude outline of an elongated structure that can be seen on the left wedge (above the galactic plane) of the galaxy distribution. It is called the Sloan Great Wall, and at 420 Mpc (1.37 billion light years), it is one of the largest structure in the universe.
Using the ingredients of regular matter (protons, neutrons, photons, neutrinos), dark matter, dark energy, and gravity, cosmologists have developed a scientific theory (the dark matter-dark energy aspect of the theory is represented by ΛCDM) to explain the observed clustering of galaxies in 3-dimensions—the Large Scale Structure of the universe. The Virgo Project, among others, has verified the ΛCDM theory through computer simulations. An example of how computer simulations can distinguish between forms of dark matter can be found here.

South Carolina State University, 01/24/2015