The Science and the Survey


In our currently favored models of the evolution of the Universe, most of the matter in the Universe is not like the stuff that you, I, this computer or the stars are made out of. Instead, it is a substance called “dark matter” so-called because it emits no light and can only interact via gravity.

In this model, when the Universe was very young, the dark matter was relatively smoothly distributed throughout the Universe, But this situation couldn’t last, because of gravity. Areas of the Universe which had just very slightly more dark matter than other areas exerted stronger gravity, pulling more dark matter towards them and causing them to get bigger, so they exerted even more gravity...this runaway effect cause all of the dark matter to start clumping together, forming what astronomers call “haloes” of dark matter.

These images and the movie are taken from the “Via Lactea” simulation. For more information on Via Lactea, visit their web-pages.

The images in the top right and top left show the expected distribution of dark matter in an area of space similar to that which the Milky Way galaxy, or the Andromeda galaxy, occupies. The first image is when the Universe is very young (roughly one-third of its current age), and the second image is what we expect the dark matter to look like now. Also shown is a movie of the evolution of the dark matter. Notice that merging of dark matter haloes occur frequently, with smaller haloes moerging together and forming bigger haloes (“hierarchical” formation). Galaxies are believed to form within these dark matter cocoons.

Galaxy Formation Models I - DARKSIDE