In the KIPAC Visualization Lab - and in major planetariums - visitors can watch three dimensional movie renderings of processes from the history of the Universe. KIPAC scientists use novel computer graphics techniques to produce and display the animations, which are based on the results from computational simulations.
Image from a movie showing a simulation of the formation of a pair of early stars, 200 million years after the Big Bang. The shading indicates the density of gas, with brighter being more dense.
Computer simulations are an invaluable tool in astrophysics, allowing scientists such as KIPAC professor Tom Abel and his group to explore processes in the Universe that we can't observe directly, like the formation of the first stars or of large scale structures far in the past. But having powerful computers perform the billions of calculations required for the simulations is only part of the challenge - the rest lies in understanding the results.
Often such understanding depends on visualizing the simulated regions of the Universe as they evolve over the course of the simulation. This is a specialized challenge because of the three dimensional spatial nature of the problem, the billions of bytes of information involved, the different size scales that may be relevant, the need to represent spatial structures that are not solid, and the finite capabilities of graphics display hardware.
KIPAC scientist Ralf Kaehler has pioneered software methods for rendering large amounts of astronomical and cosmological simulation data into useful animations and images. As a brief summary of the procedure, in the sumulation process the physical space is divided into a structure where cubes can be subdivided into smaller cubes where more resolution is necessary. The rendering process takes advantage of this subdivision heirarchy to concentrate computational resources in important regions of the space, for example where a star might be forming as opposed to an emptier patch. Then, in a technique called ray casting, for any given pixel a ray is projected from the pixel inward on a path corresponding to the observer's perspective into the simulated volume. The color and intensity of each pixel on the display is then a sum from font to back of the spatial zones intersected by the ray, with different colors and intensities corresponding to different densities and properties of the matter intersected by the ray, depending on the simulation. The technique allows the visualization of the simulated spaces to be rotated so that they be seen from different perspectives, and to be visualized in three dimensions with two different images for each eye.
The rendering of simulations into animations is useful for more than just the work of Abel's group - it is an important component of KIPAC's scientific outreach and the communication of astronomy and computation to the public. The KIPAC Visualization Lab is a miniature movie theater where everyone from school tour groups to visiting dignitaries can watch the animations in 3-D and come face to face with some of the most spectacular events in the Universe and the wonders of astrophysics, as well as the importance of cutting edge computation. Kaehler's animations, based on the simulations from Abel's group, have also appeared in planetarium shows at the Hayden Planetarium at the American Museum of Natural Histroy in New York City and the Morrison Planetarium at the California Academy of Sciences in San Francisco, narrated by Hollywood stars Whoopi Goldberg, Liam Neesen, and Jodi Foster.
Further information and some example movies are available from http://www.slac.stanford.edu/~kaehler/.