Roadrunner inspires Lab researchers to develop a new hybrid cosmology simulation code

Dark matter halos (clumps) from one of the Roadrunner simulations, with 1/64 of the total (1 gigaparsec)3 volume displayed in projection. The halos are shown as arrows, colored by their velocity magnitude. 1 parsec = 3.26 light years. This simulation was run with 64 billion particles.

August 3, 2010—Powerful cosmological surveys demand a new generation of simulations of structure formation in the Universe. Key aims include understanding why the Universe's expansion is accelerating and the composition of dark matter. Large-scale computations are an essential resource for providing detailed predictions for these observations, essential data for assisting in their design, and sophisticated tools for interpreting the final results.

Roadrunner, the world's first petaflop computing platform, inspired a new LANL-developed hybrid cosmology simulation code that uses hardware acceleration to help meet these goals. Laboratory researchers published a paper, "The Accelerated Universe" in the journal Computing in Science and Engineering, which describes their work on computational cosmology using Roadrunner. The scientists viewed Roadrunner as the entire system and designed the mesh-based cosmology code around it. The flexible algorithmic approach splits the computationally intensive pieces into local and unavoidably global pieces. The idea is to maximize the locally intensive computations, yet satisfy the inevitable latency and communication bandwidth restrictions. Successful ideas from this strategy could be used on other computer architectures.

The Roadrunner simulations showed that subtle large-scale features in the distribution of dark matter induced by the gravitational interaction with normal matter in the early Universe would be observable by cross-correlating the spectra of high redshift quasars (redshift is the amount that light is shifted toward the red end of an object's spectrum by the expansion of the universe. Astronomers use redshift as a measure of the distance of celestial objects: the higher the redshift, the greater the distance and the younger the universe when the light was emitted). These features are termed baryon acoustic oscillations. The Baryon Oscillation Spectroscopic Survey (BOSS), running on the Sloan Digital Sky Survey Telescope at Apache Point, NM, is searching for these features. One of the largest length scales to be measured by humans, the baryon acoustic oscillation signal covers a distance of about 300 million light-years. Lab scientists conducting the Roadrunner computational cosmology research include Adrian Pope and Katrin Heitmann of Space Science and Applications (ISR-1), Salman Habib and Zarija Lukic of Nuclear and Particle Physics, Astrophysics and Cosmology (T-2), David Daniel of Applied Computer Science (CCS-7), and Patricia Fasel of Information Sciences (CCS-3). LANL Laboratory Directed Research and Development (LDRD) supported the work.