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  Current Research Highlight :: October 2008 all highlights

Cosmography

The distribution of cosmic matter is only partially known since it mostly consists of mysterious dark matter, which we neither see nor know. The visible galaxies trace solely the rough outline of the highly complex network of matter concentrations and filaments, very like the lights of cities on a dark coast line permit us to imagine the countries beyond. At the Max-Planck-Institute for Astrophysics (MPA), a novel computer program for cosmic cartography was developed which permitted an international cosmography team to calculate a three-dimensional high-resolution map of our cosmic neighborhood, that shows the distribution of the invisible dark matter in great detail.

Fig. 1: Three dimensional map of the distribution of dark matter in our cosmic neighborhood in a cube the size of 1.5 million lightyears. The map was computed on the basis of the sixth data release of the Sloan-Digital-Sky-Surveys using the ARGO computer program developed at the Max-Planck-Institute for Astrophysics. The map is based on a few hundred thousand individual galaxies. (linkPfeil.gifMovie version)

The cartography of the Universe, the cosmography, is plagued by large white spots in contrast to the terrestrial cartography. Stars and dust clouds of our own Galaxy obscure many views, and the dim glow of the most distant galaxies only weakly defines the boarder areas of the observable Universe. As the geographers of medieval times one can try to fill in these white spots with assumptions. However, modern cosmography does not rely on fantasies and legends with dragons and other mythical creatures. It uses statistical methods of signal processing and well developed mathematical theories of the emergence and distribution of galaxies. Missing information cannot be drawn out of a hat with these methods, however at locations with too large gaps, stochastic methods can fill in possible cosmic landscapes, which at least have correct statistical properties.

Maps of the Universe constructed in this way, are of great scientific value, less for the purpose of cosmic navigation, since intergalactic journeys even with the speed of light would require millions to billions of years, but more to study the structure and evolution of the Universe.

The seeds of the visible structures today were sown in a fraction of the very first second of the Universe. In the following fourteen billion years these structures grew constantly. They are therefore a window into the early epochs of the universe, shortly after the big bang, when space was filled with radiation and hot plasma and there were neither stars nor galaxies. An analysis of these structures reveals properties of cosmic matter, gravitation, which is responsible for the structure growths and the geometrical properties of space-time of the Universe. Good cosmic maps permit further detailed predictions of a number of observable effects. Comparing them to real observations may verify our understanding of space, time and matter.

The construction of such maps was so far a huge computational problem, since in principle each galaxy brings a bit of information for each of the millions of positions of the reconstructed Universe. Earlier attempts to construct such maps required enormous computations on supercomputers, but delivered only maps with moderate resolution. Jens Jasche and Francisco S. Kitaura of the cosmography team at MPA have developed ARGO (Algorithm to Reconstruct Galaxy-traced Overdensities), a computer program, which is able to generate within an hour on an ordinary personal computer three dimensional maps with, compared to earlier works, significantly increased resolution. Cheng Li, also of the cosmography team at MPA, and Francisco S. Kitaura have prepared data from the Sloan-Digital-Sky-Survey for the data processing. Thus the team of scientists succeeded at calculating the probably most detailed map of the Universe ever. It shows the distribution of dark matter in a cube the size of a 1.5 billion light-years in our cosmic neighborhood.

The high speed with which ARGO generates maps will in future permit us to combine the steadily growing number of measured galaxies into a common, high-resolution chart of the visible Universe. Simultaneously, any existing uncertainties due to measurement inaccuracies will be characterized precisely. Thereby, the maps become applicable for solid scientific purposes.

For example, Torsten Enßlin, who initiated the cosmography project, is planning to use such maps for predictions of the temperature fluctutations of the cosmic microwave background radiation, which are generated by the rip-off of matter structures in the accelerated expanding Universe today. Presumably in 2009, the Planck-Surveyor satellite mission will accurately measure such fluctuations. The observations can then be compared to the predictions, permitting us to measure the rate of cosmic acceleration more precisely.

Although the cosmographic maps are meant for pure scientific purposes, in the unlikely case that a traveler wants to use them to navigate through the Universe, the cosmography team wishes him a comfortable journey for the next million years.


Franciso S. Kitaura, Jens Jasche, Cheng Li, Torsten A. Enßlin


Further Members of the Cosmography Team:

Ben Metcalf, Gerard Lemson, Benjamin D. Wandelt, Jérémy Blaizot

Involved Institutions:

Max-Planck-Institut für Astrophysik, Garching (JJ, FSK, CL, TAE, SDMW, JB, BM)
Max-Planck-Institut für Extraterrestische Physik, Garching (GL)
Scuola Internazionale Superiore di Studi Avanzati di Trieste (FSK)
Université de Lyon (JB)
University of Illinois at Urbana-Champaign (BDW)

Publications

The cosmographic map is based on the method described in
F.S. Kitaura and T.A. Enßlin, "Bayesian reconstruction of the cosmological large-scale structure: methodology, inverse algorithms and numerical optimization", 2008, linkPfeilExtern.gif Monthly Notices of the Royal Astronomical Society Volume 389, Issue 2, pp. 497-544.



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last modified: 2008-10-13