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Missing matter mystery in small galaxies

Diminutive they may be, but the smallest galaxies seem most able to muscle out visible matter, and so are darker than their larger cousins. This deepens a mystery about where all of the universe's visible matter has gone.
Ordinary matter - the zoo of protons, electrons, and other particles we see around us - is thought to make up just 4 per cent of the universe, with the rest being dark matter and dark energy. But inventories of the stars and gas in the nearby universe have revealed only about half the matter that is predicted by cosmological models.
Now there's another twist in the mystery: it seems pint-sized galaxies hold even less matter than expected. The smaller a galaxy, the smaller its proportion of normal matter to dark matter, says Stacy McGaugh of the University of Maryland in College Park, who presented a census of the contents of galaxies at a meeting of the American Astronomical Society in Washington DC last week.

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An international team of scientists, led by University of Maryland astronomer Stacy McGaugh, has found that individual galactic objects have less ordinary matter, relative to dark matter, than does the Universe as a whole.
Just published in the Astrophysics Journal (e- version), these results were presented by McGaugh today during a press conference at the American Astronomical Society Meeting in Washington, D.C.
Scientists believe that all ordinary matter, the protons & neutrons that make up people, planets, stars and all that we can see, are a mere fraction -- some 17 percent -- of the total matter in the Universe. The protons and neutrons of ordinary matter are referred to as baryons in particle physics and cosmology.
The remaining 83 percent apparently is the mysterious "dark matter," the existence of which is inferred largely from its gravitational pull on visible matter.
McGaugh and his colleagues posed the question of whether the "universal" ratio of baryonic matter to dark matter holds on the scales of individual structures like galaxies.

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Title: The Baryon Content of Cosmic Structures
Authors: Stacy S. McGaugh, James M. Schombert, W.J.G. de Blok, Matthew J. Zagursky
(13 Nov 2009)

We make an inventory of the baryonic and gravitating mass in structures ranging from the smallest galaxies to rich clusters of galaxies. We find that the fraction of baryons converted to stars reaches a maximum between M500 = 1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright galaxies in groups. The fraction of baryons detected in all forms deviates monotonically from the cosmic baryon fraction as a function of mass. On the largest scales of clusters, most of the expected baryons are detected, while in the smallest dwarf galaxies, fewer than 1% are detected. Where these missing baryons reside is unclear.

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Heterogeneous Universe Model: an alternative to dark energy

Depuis les débuts de la cosmologie moderne utilisant la théorie de la relativité générale, les seuls modèles retenus pour décrire la géométrie et la dynamique de l'Univers étaient spatialement homogènes. La formation des structures à grande échelle était obtenue par perturbation linéaire de ces modèles, ce qui impliquait comme hypothèses que les fluctuations de densité et la courbure étaient très faibles, d'où les difficultés à former les structures avec la rapidité voulue. A l'ère de la cosmologie dite ''de précision'', l'hypothèse d'homogénéité -- qui a servi à développer avec succès les bases de la cosmologie -- doit être considérée comme une approximation d'ordre zéro et la théorie des perturbations linéaires comme une approximation du premier ordre. Si l'on veut aller plus avant, on ne peut plus ignorer l'influence des inhomogénéités observées à toutes les échelles, en commençant bien sûr par les plus grandes. L'utilisation de solutions hétérogènes de la relativité générale est donc devenue incontournable. Dans ce domaine en pleine expansion, une chercheuse de l'Observatoire de Paris en collaboration avec deux chercheurs polonais et un chercheur d'Afrique du Sud ont obtenu des résultats très intéressants.
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Name   RA         Dec      z
CL0016  00 18 33.4 16 26 14 0.5471+0.0032
Clump 1 00 17 40.2 16 24 59 0.5474+0.0004
Clump 2 00 17 58.9 16 23 28 0.5512+0.0007
Clump 3 00 18 16.4 16 14 02 0.5482+0.0020
Clump 4 00 18 17.4 16 17 39 0.5493+0.0015
Clump 5 00 18 43.7 16 33 17 0.5509+0.0012
Clump 6 00 18 47.6 16 02 14 0.5409+0.0007
Clump 7 00 19 06.5 16 53 02 0.5447+0.0007
Clump 8 00 19 17.6 16 48 29 0.5568+0.0005
Clump 9 00 19 22.2 16 24 32 0.7278+0.0019
Clump10 00 19 25.7 16 05 23 0.5427+0.0004
Clump11 00 19 31.5 16 27 44 0.6253+0.0001
Clump12 00 19 32.4 16 02 03 0.6264+0.0003
Clump13 00 19 47.9 16 28 11 0.5445+0.0006
Clump14 00 19 53.3 16 36 02 0.5584+0.0009
Clump15 00 19 58.4 16 46 58 0.5425+0.0003
Clump16 00 20 10.4 16 25 21 0.5550+0.0004
Clump17 00 20 29.9 16 33 23 0.5443+0.0010


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Title: The spectroscopically confirmed huge cosmic structure at  z = 0.55
Authors: M. Tanaka, A. Finoguenov, T. Kodama, Y. Koyama, B. Maughan, and F. Nakata

We report on the spectroscopic confirmation of a huge cosmic structure around the CL0016 cluster at z=0.55. We made wide-field imaging observations of the surrounding regions of the cluster and identified more than 30 concentrations of red galaxies near the cluster redshift. The follow-up spectroscopic observations of the most prominent part of the structure confirmed 14 systems close to the cluster redshift, roughly half of which have a probability of being bound to the cluster dynamically. We also made an X-ray follow-up, which detected extended X-ray emissions from 70% of the systems in the X-ray surveyed region. The observed structure is among the richest ever observed in the distant Universe. They will be an ideal site for quantifying environmental variations in the galaxy properties and effects of large-scale structure on galaxy evolution.

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Shedding Light on the Cosmic Skeleton
Astronomers have tracked down a gigantic, previously unknown assembly of galaxies located almost seven billion light-years away from us. The discovery, made possible by combining two of the most powerful ground-based telescopes in the world, is the first observation of such a prominent galaxy structure in the distant Universe, providing further insight into the cosmic web and how it formed.

"Matter is not distributed uniformly in the Universe. In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called 'cosmic web', in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure" - Masayuki Tanaka from ESO, who led the new study.

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Is the matter in the universe arranged in a fractal pattern?
A new study of nearly a million galaxies suggests it is though there are no well-accepted theories to explain why that would be so.
Cosmologists trying to reconstruct the entire history of the universe have precious few clues from which to work. One key clue is the distribution of matter throughout space, which has been sculpted for nearly 14 billion years by the competing forces of gravity and cosmic expansion. If there is a pattern in the sky, it encodes the secrets of the universe.

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