SCIENCE

Scientists relied on NSF TeraGrid computing resources at Pittsburgh Supercomputing Center to create the finale of a thrilling new planetarium show for the American Museum of Natural History. - "Two spiral galaxies, spinning like jeweled spiders, approach, flow through each other, separate as arms of stars flow gracefully akimbo and then draw together again in a double-yoked embrace . . . ." This poetic prose in the New York Times (by science writer Dennis Overbye) describes the grand finale of "Cosmic Collisions," a space show now playing at the American Museum of Natural History (AMNH), New York City. The scene, a simulation that depicts the Milky Way and Andromeda galaxies colliding and eventually merging five billion years from now, owes its existence to the computational horsepower of LeMieux, a terascale (trillions of calculations per second) computing system at the Pittsburgh Supercomputing Center. A lead computing resource of the National Science Foundation TeraGrid, LeMieux is a massively parallel supercomputing system. It uses many processors teamed to work together to carry out large-scale research projects in many fields of science that rely on computation. For the galaxy collision segment of "Cosmic Collisions," physicist Mordecai-Mark Mac Low of the American Museum of Natural History and his colleagues - Yuexing Li of Columbia University and Ralf Klessen of the Astrophysikalisches Institut Potsdam, Germany - used LeMieux to simulate in precise scientific detail how a "globular cluster" galaxy forms from the merger of two galaxies, such as Milky Way and Andromeda, that are near to each other in space and gravitationally attracted by each other. "With LeMieux," says Mac Low, "we were able to do complex calculations in less than a month that would have required more than four years on a single powerful desktop computer." Their simulation used 64 processors of LeMieux (of 3,000 available) to calculate the behavior of stars, gas and dark matter in the galaxies. It modeled the force of gravity distributed across millions of virtual particles and tracked pressure changes and the movement of shock waves in the gas. Robert Redford narrates "Cosmic Collisions," and during the final scene, to a backdrop of music composed for this show, he explains that many galaxies are formed by collision and merger with other galaxies. As the AMNH website points out, if distances were shrunk so that the sun were a grain of sand, it would still be four miles from its nearest neighbor star. If the Milky Way, composed of billions of stars, however, were a grain of sand, it would be only a fraction of an inch from the Andromeda galaxy. AMNH distributes "Cosmic Collisions" nationally and internationally and expects that it will reach millions of people. Along with the galaxy collision finale, the show depicts the face of the sun as it ejects material toward Earth, the creation of the Moon, the collision of two stars and a meteorite impact with Earth. "Cosmic Collisions" uses simulations from a number of scientists and its visualizations are based on the most up-to-date scientific knowledge. The galaxy merger simulation by Mac Low and colleagues was reported in The Astrophysical Journal, Oct. 10, 2004. Their simulation is the first such study to track individual star clusters and follow them on their orbits during a galaxy merger, and their results support hypotheses that merger processes explain the origin of dense clusters of stars in certain galaxies, such as have been observed by the Hubble Space Telescope in the past decade. "Cosmic Collisions" was developed by the American Museum of Natural History, New York, in collaboration with the Denver Museum of Nature & Science; GOTO, Inc. (Tokyo) and the Shanghai Science and Technology Museum and created by AMNH with major support of from NASA and CIT. For background information, including graphics on "Cosmic Collisions" see: its web site. The Pittsburgh Supercomputing Center is a joint effort of Carnegie Mellon University and the University of Pittsburgh together with Westinghouse Electric Company. Established in 1986, PSC is supported by several federal agencies, the Commonwealth of Pennsylvania and private industry, and is a leading partner in the TeraGrid, the National Science Foundation's cyberinfrastructure program.