Archivi tag: Large-scale Structures

Drifting through the Cosmic Web

The Large Scale Structure of the Universe (LSS) was first discussed at the IAU Symposium No. 79 in 1977 in Tallinn. The title of the Symposium : “The Large Scale Structure of the Universe” , was the first official use of this term (J. Einasto). Since then, it has been of major interest in cosmology. This large scale pattern, emerged from the primordial density fluctuations of dark matter under the effect of gravity, is composed of nodes, filaments and walls surrounding large voids: it is a vast foam-like structure, aka the “cosmic web”, which provides constraints on the content of the universe and the nature of its components. Continua a leggere Drifting through the Cosmic Web


Statistical Challenges in 21° Century Cosmology

In the era of large astronomical surveys that are grappling with unsolved methodological and data challenges, transforming Data into Science is a huge, and exciting, problem. With surveys and instruments such as Planck, Pan-STARRS1, DES, VST KiDS, LSST, Gaia, EUCLID, JPAS, SKA, wide-field spectroscopic surveys and the large and interconnected databases of archival material coming online, a special scientific focus on cosmological inference is of great interest. Without this focus there is no guarantee that the best possible Science will be the outcome of this data-flood. But transforming data into knowledge is still a largely unsolved problem; a problem, that must be tackled by cross-disciplinary efforts.

Continua a leggere Statistical Challenges in 21° Century Cosmology

From dark matter to galaxies

Recent years have witnessed the establishment of the concordance cosmology. Under the Cold Dark Matter scenario,  cosmic structures are characteristic of dark matter haloes embedded in the cosmic web. Galaxies are thought to form at the center of dark matter haloes via gas cooling and fragmentation. Various models and numerical simulations have been developed to model the formation and evolution of galaxies. Observations of the galaxy population and local group are used to constrain the cold dark matter model on large and small scales. 
Continua a leggere From dark matter to galaxies

Exploring the dark sector of the Universe with supercomputers

L’Universo è composto dal 95% di energia scura e materia scura. Comprendere la fisica del cosiddetto “settore scuro” rappresenta la principale sfida della cosmologia moderna. Oggi, grazie a sofisticate simulazioni numeriche, possiamo iniziare a comprendere l’evoluzione dell’Universo primordiale e la formazione delle strutture cosmiche.

The primary lens through which scientists look at the night sky is no longer only a telescope, it’s also a supercomputer. The new and coming generations of supercomputers will finally be capable of modeling the Universe in the detail and volume required by astronomical surveys of the sky that are now underway, or soon will be. Scientists use large cosmological simulations to test theories about the structure of the Universe and the evolution of the distribution of galaxies and clusters of galaxies. State of the art supercomputers let cosmologists make predictions and test them against data from powerful telescopes and space probes. Two decades of surveying the sky have culminated in the celebrated Cosmological Standard Model. Yet two of the model’s key pillars, dark matter and dark energy, together accounting for 95% of the Universe, remain mysterious. A research team led by Argonne is tackling this mystery, aided by some of the world’s fastest supercomputers. To model the distribution of matter in the Universe, the researchers are running some of the largest, most complex simulations of the large-scale structure of the universe ever undertaken.The Argonne team has run a 1.1-trillion-particle simulation on half a million processor cores of Mira, Argonne’s new Blue Gene/Q supercomputer. The team was among a few science teams from across the country to gain early access to the system, which is now online.

“In a very real sense, we only understand 4% of the Universe. To basic scientists like us, that’s a crime—that’s not allowed”, says Argonne physicist Steve Kuhlmann.

The power and speed of supercomputers and simulation codes  have significantly advanced over the past decade. Mira enables cosmology runs with greater resolution and accuracy on much larger simulation volumes, giving researchers the ability to confront theory with observational data from wide-area cosmological surveys. Exploring the cosmic structure of the dark Universe is an enormously complex problem. As the Universe expands, gravitational attraction causes matter to coalesce and form structures, first sheets, then filaments where the sheets intersect, and then clumps where the filaments meet. As time progresses, one can begin to see more clearly the basic structure of an enormous web of voids, filaments, and clumps. Simulations at Argonne have calculated this web-like structure, the so-called cosmic web, in a cube of simulated space more than 13 trillion light-years across. “Because these trillions of particles are meant to trace matter in the entire universe, they are extremely massive, something in the range of a billion suns”, said Argonne computational physicist Salman Habib, the project’s director. “We know the gravitational dynamics of how these tracer particles interact, and so we evolve them forward to see what kind of densities and structure they produce, as a result of both gravity and the expansion of the Universe. That’s essentially what the simulation does: it takes an initial condition and moves it forward to the present to see if our ideas about structure formation in the Universe are correct”.

Dark energy may be the most profound mystery in all of science”, says University of Chicago cosmologist Michael Turner.

Next-generation sky surveys will map billions of galaxies to explore the physics of the “dark universe”. Science requirements for these surveys demand simulations at extreme scales in order to resolve galaxy-scale mass concentrations over the observational volumes of sky surveys. A key aspect of the Argonne project involves developing a major simulation suite covering approximately 100 different cosmological scenarios and combining them in a framework that can generate predictions for any scenario within the range covered by the original runs.

ANL: Exploring the dark universe at the speed of petaflops

ANL: Dark energy: Q&A with Steve Kuhlmann

CosmicConference – Domenica 1° Dicembre ore 18

Il 96% dell’Universo


Exascale Radio Astronomy

The topics covered by the next-generation of radio telescopes will touch upon cosmology, dark ages, epoch of reionization, galaxy evolution, dark energy, dark matter, general relativity, cosmic magnetism, and pulsars etc.

Why Exascale Radio Astronomy? (PDF)