Dark matter between galaxies?

The movements of galaxies within the clusters showed similar problems than with the rotation of stars in galaxies. This suggests the presence of dark matter between the galaxies; although nothing proves yet that these two problems are related. On a galaxy scale, the dark matter rate would be up to 10 times that of the luminous matter, but on the clusters' level, it would be much more important: up to 30 times the "visible" mass of these clusters.

In 1996, astrophysicist Yannick Mellier and his team decided to measure the quantity of dark matter in all the Universe and to draw up a chart of its distribution between the galaxy clusters. The method used was to make a large scale statistical study of the galaxy deformation due to gravitational interaction of dark matter existing between the Earth and these clusters. This gravitational intercation is visible as it deviates the luminous rays sent by the galaxies (their image arrives deformed). A statistical study on a very large scale (the area of the sky studied was the apparent size of the moon and on a depth of 5 billion light-years) made it possible to neglect the local deformations due to other galaxy clusters.

This study led in March 2000 to the a cartography. The dark matter takes the shape of long intersecting filaments. The quantity of matter of the universe should represent one third of that needed to reach the critical density, the remainder made up of dark energy.

A new similar study is in hand, always by the team of Yannick Mellier, with this time a larger CCD camera, allowing the study of 20 times the previous field of view.

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Introduction First observational evidences The galactic rotation problem
Dark matter within galaxies Dark matter between galaxies Dark matter Composition
Baryonic Nonbaryonic Neutrino WIMP String theory