The large scale filamentary structure (367 kb)
The second part of the sequence covers the collapse of structure in the universe from the smaller scales considered in cosmology (about 10 Mpc) down to the larger scales connected with galaxies (about 5 kpc). A particle based simulation by Frank Summers (Princeton University) follows the non-linear growth of density perturbations under a generic model of hierarchical structure formation. A richly detailed picture develops which connects the interwoven collapse processes of the condensation of large scale filaments, the quiescent as well as violently merging formation of galaxies, and the aggregation of galaxies into groups and clusters.
The computer simulation used a combined N-body plus smoothed particle hydrodynamics (SPH) code and followed the evolution of 2.1 million dark matter particles and 2.1 million gas particles. This simulation is the largest cosmological SPH simulation performed to date and provides unprecedented dynamic range in depicting the galaxy formation process. Visualization of the data was done at NCSA using some innovative techniques. Of special note is Virtual Director, a new system for choreographing camera shots through three dimensional evolving data sets that operates in NCSA's virtual reality environment, the CAVE. A proprietary program for rendering the large and complex data sets was written at the computer graphics and special effects company, Pixar.
This part of the sequence is divided into 3 camera shots. The first shot is a large scale overview showing the early formation of what cosmologists call `filamentary structure'. The filaments are interconnected in diverse and manifold ways such that overall picture resembles a delicate web. Galaxies form in the knots along these filaments and the second shot illustrates this idea by traveling along a filament. Several galaxies in formation pass into view and one can follow the gravitational dance as several clouds of gas and stars orbit each other and merge. The final shot demonstrates that clusters of galaxies form at the intersection of filaments, as galaxies from several filaments drain into a densely populated region. The interwoven motions of galaxies are especially complex here and many mergers and tidal interactions occur. Passing through the cluster, we set the stage to focus on a high resolution simulation of a galaxy merger in the third part of the structure formation sequence.
These images are still renders used to help design camera moves for the galaxy formation sequence in the film. The images are just `quick looks' at the data and do not represent any final choices. What they do convey is the incredible richness of structure in the simulation. The color map is simplistic: the gas particles in the simulation are colored red and the star particles are white.
Credits: Frank Summers (Princeton), Donna Cox, Robert Patterson, Erik Wesselak, and Barry Sanders (NCSA). The rendering program was written by Loren Carpenter at Pixar.
NOTE: There are subtle details in these images, especially in the gas. For best results, try changing the intensity curve of the color display to suit your monitor. For those familiar with the jargon, play with the gamma value. In the program "xv", use the "ColEdit" button.
The large scale filamentary structure (367 kb)
A simulated galaxy in formation (85 kb)
A group of simulated galaxies in formation (120 kb)
Simulated galaxies about to collide within a cluster of galaxies (126 kb)