Computer simulations unlock the mysteries of the Universe
As part of the "Horizon ProjectI", a team of French scientists, led by Romain Teyssier, Astrophysicist at CEA, has completed the largest simulation ever carried out of structure formation in the Universe. This simulation, which used the new Bull supercomputer at the Research and Technology Computing Center (CCRTII), will enable astrophysicists to compare their models with astronomical observations with unprecedented realism.
Credit C. Pichon, D. Aubert.
13, 2007 -
The great advances achieved recently in computer science imply ever-greater leaps in scientific progress. In Astrophysics, solving the equations of fluid mechanics using more effective algorithms and increasingly more powerful supercomputers helps us to understand how structures form in the universe. "Starting from the initial conditions of our universe, that can be observed directly on the Cosmic Microwave BackgroundIII, it is possible to compute individual trajectories of a large numbers of particles in order to describe the cosmological fluid," explained Romain Teyssier.
With nearly 70 billion particles and over 140 billion meshes, the computation performed at the CCRT is an absolute record for a simulated N-body systemIV. For the first time in the history of high performance computing, it is possible to simulate half the observable universe, while being able to resolve a galaxy like the Milky Way with more than hundred particles!
To simulate such volumes in such detail, the Horizon team ran the "RAMSES" code on the 6144 Intel® Itanium2® processors of the Bull NovaScale 3045 supercomputer recently installed at CCRT. This code, developed at CEA in conjunction with astrophysicists of the Horizon Project, makes use of an adaptive gridV that provides unprecedented spatial resolution (equivalent to a cubic grid with side length of 262,144 grid points!). Thanks to experts of Bull and CCRT, the program took full advantage of the computer resources for nearly two months, using over 18 Terabytes of RAM and generating approximately 50 Terabytes of data to disk. The same project, performed on a personal computer, would have required more than thousand years to complete!
"With this new simulation, we will be able to predict how matter is distributed in the Universe with great precision and realism," continued Romain Teyssier."We will soon be in a position to compare our model with full-sky observations, such as the one that will be shortly available thanks to the Planck space mission that will be launched by the European Space Agency in 2008. We will also be able to prepare future experiments on gravitational lensingVI, such as the "Dark UNiverse Explorer", a new project for determining the nature of dark energy."
I Horizon Project: This is a joint project between CEA, CNRS and French universities which brings together around twenty science and teaching staff, experts in digital simulation and in structure formation of the universe. For more details, see http://www.projet-horizon.fr.
II CCRT: this high performance computing center is located at the CEA-DAM Ile-de-France site and is part of the CEA's supercomputing complex. It boasts a computing power of over 50 TeraFlops, thereby allowing CEA and its academic and industrial partners (EDF, Safran, Onera and EADS/Astrium) to rise to scientific and industrial challenges entailed in their high performance digital simulation projects.
III This radiation is the fossil record of the Universe from the time that it finally became transparent to light, when it was 380,000 years old. This light reaches us 13 billion years later, and tells us about the conditions that prevailed back then in the cosmological plasma.
IV An "N-body system" is a set of material points, or "particles" that are subject to mutual gravitational attraction. Powerful computers are needed to calculate the trajectories of each particle in such N-body systems.
V To solve the equations of fluid mechanics on a computer, it is necessary to discretize space into small volume elements or "cells". A large set of cells, known as the "grid" or the "mesh", is the actual system we want to describe, in our case a large section of the Universe. To make the calculation more precise, we use smaller cells in dense regions such as galaxies: the grid automatically adapts to local conditions, hence the term "adaptive grid".
VI The light from the background galaxies is deflected by the gravitational mass along its path. This gravitational lensing effect, predicted by Einstein's theory of relativity, can be used to measure the quantity of matter between these galaxies and the Earth, and thus to test our theory of structure formation in the Universe.
About the CEA
The CEA (France's Atomic Energy Authority, Commissariat à l'Énergie Atomique) is a major public sector player in technology research. The CEA operates in three main areas: energy, information technology and healthcare, defense and security, building on its excellence in fundamental research.
As a major player in the European research landscape, with renowned international expertise in its specialist fields, the CEA cultivates many collaborative initiatives with international partners.
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