A group of astronomers believe to have discovered a flaw in the model of cold dark matter, explaining the formation of galaxies. Recent observations on the dwarf galaxies orbiting the Milky Way could be explained only by giving up the theory of dark matter in favor of modification of the law of the gravitation of Newton to large scales.

In recent years, observations supporting the existence of dark matter have accumulated and the Mond theory proposed to account for the abnormally rapid behavior of stars in galaxies and galaxies in clusters of galaxies is losing ground. This theory, rather than to invoke a dark matter of an unknown nature, introduced a modification to the Newton’s law of gravitation on a large scale, which would no longer be 1/r2.

Theories based on extensions of general relativity theory of gravitation proposed by Einstein in 1916, exist. Some of them seem to actually be able to agree to some extent with the observations. One of the most famous is the one proposed by John Moffat, for example, observations of collisions of galaxy clusters. It seems that even if modifications to the law of Newton are indeed valid at large distances, a dark matter component can not be ruled out as main explanation anyway.

Some astrophysicists remain perplexed or dubious. The German astronomer believes that the comments that he and his colleagues have made on the dwarf galaxies orbiting the Milky Way, like the Dragon or Sagittarius may not be compatible with the models of cold dark matter.

You should know that dwarf galaxies are a problem for astrophysicists and cosmologists partisan models of galaxy formation based on cold dark matter for some time. These describe the formation of large galaxies and clusters of galaxies, congregating in large structures and come into collision. But these models also predict a large number of dwarf galaxies around large galaxies like ours or that of Andromeda.

A map of some of the dwarf galaxies orbiting the Milky Way

Why dwarfs form a disc?

As they are not so bright, these dwarfs are more easily detectable around the Milky Way. The problem is that the models predict a hundred of it and the observations however led with rigor and determination to persist would be a half. The situation has just worsened according to the group of international researchers including Kroupa and Metz.

Indeed, dwarf galaxies which are bright are not uniformly distributed around the Milky Way. They form a disc and orbit in the same direction as that of stars in the Galaxy. However, this provision and this movement does not seem possible that if the dwarf ones come from the tidal interactions during collisions between the Milky Way and other galaxies. Digital models of celestial mechanics indicate that they would have formed recently and they were poor in dark matter. But this conclusion is in contradiction with other observations that indicate the contrary, they contain rather large quantities … unless it is precisely the law of Newton that has to be changed!

Several intermediate mechanisms and assumptions come into play in the modeling of these phenomena on the scale of galaxies. In this case, it would be premature to conclude that these observations really refute the theory of dark matter. It would however not be wise to neglect them either.

Some astrophysicists believe that everyone could be right. For some situations, only the dark matter would be a satisfactory explanation, but in other theories as Mond, it demonstrates their relevance. In all the cases, it is necessary to call upon new physics. That can only delight the theorist…

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