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By Trish Barker A simulation devised by researchers at UCSD shows how energy rippling out from quasars ionized the intergalactic medium of the universe The universe is so vast and vastly old that it seems to defy observation, explanation, and imagination. Scientists can't put the universe under a microscope or create stars and galaxies in test tubes. Rather than throwing their hands up in despair, cosmologists turn to calculation and simulation to answer fundamental questions about the history and evolution of the universe. As NCSA director Dan Reed testified to the U.S. House Science Committee in July, "One of the unique capabilities of large-scale scientific simulation [is] the ability to model phenomena where experiments are not otherwise possible." Quasars are among the phenomena that simulation is helping to demystify. Discovered just 40 years ago, quasars are prodigious energy producers. Although they are not much bigger than our solar system, quasars pour out 100 to 1,000 times as much light as a galaxy containing a hundred billion stars. Spinning black holes are thought to be the engines powering quasars. The prevailing theory is that the spinning draws streams of gases spiraling into the black hole's center, just as an eddy in a stream pulls water into its depths. As these gas streams collide, intense friction results; vast amounts of heat and energy are emitted before the gases finally collapse into the black hole. Quasars are believed to be this final blast of energy. All of the quasars that have been identified are billions of light-years away, so their energy has traveled immense distances to reach our solar system. Therefore, observing quasars is a way for cosmologists to travel back in time. It’s similar to the way paleontologists study our planet’s past by digging down through layers of earth, uncovering fossils that provide clues about the animals and plants of long-past epochs. Just as paleontologists use fossilized bones to build theories about the muscle, skin, characteristics, and behavior of dinosaurs, cosmologists use the clues gathered through observation to envision, simulate, and build theories about the evolution of the universe. Michael Norman, professor of physics and director of the Laboratory for Computational Astrophysics at the Center for Astrophysics and Space Sciences at the University of California at San Diego (UCSD), has traveled back to one era of the universe. Norman's research team used NCSA's Titan cluster to complete a ground-breaking simulation of how ultraviolet radiation from quasars propagates through intergalactic space, reionizing helium gas.
Access Online | Posted 11-18-2003 |
A volumetric rendering of the distribution of intergalactic gas. Quasars, which ionize the gas with their ultraviolet radiation, are introduced into this volume. |
