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The Works!

Adding Gas Physics, Radiation, and Galaxy Formation

Cosmologists at Princeton University and elsewhere are attempting to bring even greater complexity and resolution into their models, taking advantage of the exponential advances in computer memory and speed. In addition to modeling cosmic evolution in all three spatial dimensions, the codes they are developing incorporate not only dark matter and gas hydrodynamics but also some of the essential physics of galaxy formation itself.

Jeremiah Ostriker, Princeton University, on-camera
Movie/Sound Byte
QuickTime Movie (1.5 MB); Sound File (763K); Text

This requires adding physics at the atomic scale. Although radiation was liberated from matter following recombination, the photons and gas were still in close proximity, so there were a lot of collisions. The initial collisions slowed the rate of cooling of matter. As matter cooled, quasars, star clusters and, later, galaxies began to form, much as crystals precipitate out of a cooling solution. These structures themselves became local "hot spots," ionizing nearby gases by collisions and radiation (in which hydrogen and helium nuclei are stripped of their electrons and become electrically charged) and inhibiting further "precipitation" of matter into structures. The interaction of the cosmic background radiation, as well as the radiation emitted from structures such as galaxies and quasars, with matter therefore determines not only how and where galaxies emerge from the gas, but also how and where the first stars are born as the cosmos evolves.

Jeremiah Ostriker, Princeton University, on-camera
Movie/Sound Byte
QuickTime Movie (1.7 MB); Sound File (854K); Text

Both physics and dynamics must be modeled across a hierarchy of scales, from the giant clusters of gas from which galaxy superclusters condense to the birth of single galaxies within them. The Princeton team, led by Jeremiah Ostriker, has tested cold plus hot dark matter models and found them wanting, so they are developing codes that ignore "hot dark matter," testing instead how "cold" dark matter alone interacts with cosmic gas to form galaxies.

Resolving all the major physics of cosmic evolution across all scales of the universe is beyond the performance of present-day computers. Doing so will require orders of magnitude more sustained speed and memory.

However, it is still unlikely that advances in hardware alone will permit numerical cosmologists to compute the cosmos across all scales of space. They'll also need new kinds of software, including codes that can run across a variety of computer platforms as a single application and adaptive multiscale algorithms to compute and visualize a digital universe across multiple scales of space.

All Inclusive and Testing
Ramping Up the Resolution

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Copyright, (c) 1995: Board of Trustees, University of Illinois

NCSA. Last modified 10/9/95.