Two-dimensional visualizations of dark matter structure, such as images and movies, have the shortcoming that the actual density field has to be projected along one dimension. In order to visualize the true, three-dimensional density field, we created surfaces and translated them into 3D-printed structures. This work was performed in collaboration with Isaac Facio from the School of the Art Institute of Chicago in the context of our art project The Fabric of the Universe.
In 2D images, we can use a color scale to express the density of dark matter, but in 3D printing, we have only one surface of one color available. We chose this surface to be a 3D iso-density contour at roughly the mean density of the universe. The images below refer to a simulation with side length 125 Mpc/h (see Diemer & Kravtsov 2014 for details). The resulting surface, however, is very complex as shown in the left panel:
3D printers have a limited resolution, meaning we cannot print infinitesimally small structures. Thus, we apply a Gaussian smoothing to the density field before creating the surface (center panel). Finally, we find the largest connected structure and remove all smaller structures (right panel). The photo below shows the 3D-printed object.
Furthermore, we studied the infall region around the most massive cluster halo in the simulation (shown below). This object highlights the advantage of 3D printing as a visualization technique: the structure contains large walls of infalling dark matter that are not visible in 2D visualizations. If such a wall intersects a 2D image, it shows up as a filamentary structure instead.
The 3D surfaces shown here are publicly available as print-ready .stl files (cosmological_volume.stl, infall_region.stl). If you use them in a publication or exhibition, please credit our art & science collaboration The Fabric of the Universe for the 3D models.