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Pure Dark Matter

Because astronomers have deduced that dark matter is the dominant form of matter in the universe, numerical cosmologists first constructed codes to predict how large scale structures are formed by the gravity of dark matter alone. Despite the fact that the resulting structures can't be observed directly, by assuming that "mass follows light," they do provide a strong indication of how luminous (baryonic) matter would cluster.

Numerical cosmologists have explored various mixtures of cold and hot dark matter, which cluster in different ways. Hot dark matter forms large coherent filaments, whereas cold dark matter produces hierarchically clustered objects--like the real universe. One class of calculations performed on pure dark matter models are scale-free. Scale-free studies, while not true cosmological models, provide a convenient abstraction of realistic power spectra in two simple parameters which are easy to characterize and explore.

In such simulations, numerical cosmologists trace the gravitational interactions of "mass clouds" of dark matter particles within grid boxes. This approach, called a particle-mesh algorithm, allows the cosmologists to calculate the force exerted on groups of mass clouds by other mass clouds. As the clouds move in response to each other's gravity, the density distribution changes too, which in turn alters the movements of the clouds.

Featured below are three types of scale-free, pure dark matter simulations, each containing greater complexity.

2-D Scale-Free, Particle-Mesh
3-D Scale-Free, Particle-Mesh, Particle-Particle
3-D Scale-Free, Higher Resolution

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NCSA. Last modified 10/7/95.