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Little dark matter in the early galaxies.

The analysis of the speed of rotation of six distant galaxies made with the Very Large Telescope has determined that the first galaxies of the universe, dating back some 10 billion years ago, contained much less dark matter than at present

Unlike current galaxies, the first galaxies that formed in the universe consisted mainly of stars and gas, and not as dark matter. The confirmation of this hypothesis comes from the study of researchers from the Max-Planck Institute for Extraterrestrial Physics in Garching, Germany, who sign an article in “Nature”.

In the seventies, astronomers discovered that stars that are found in the outer parts of some galaxies appear to be moving at a speed that would make her escape from their galaxy if they were subject only to the gravity of the visible mass. To this it was speculated, that most of the mass of the galaxies was formed by some form of matter not directly observable, the so-called dark matter, the nature of which even today is discussed. The evolution models predict that at the time of the formation of today’s massive galaxies, about 10 billion years ago, they were composed mainly of gas and stars. (The massive galaxies are galaxies that have at least a mass of about one hundred billion solar masses, like the Milky Way, unlike the dwarf galaxies that come to more than a few billion solar masses.) The prevalence of stars and gas during training of these galaxies it stems from the fact that the ordinary matter interacts more strongly with the surrounding environment of the elusive dark matter, and then focuses more quickly. The aggregation of dark matter in galaxies requires rather more time.

In this case, the internal disks of distant galaxies – which we see as they were in the distant past, and then, when they were younger – should contain a larger fraction of stars and gas than those of nearby galaxies, which are therefore also temporally closer to us and they have had more time to aggregate dark matter. To check this model, astrophysicists have studied six distant galaxies in the universe, that is ancient, with K-band Multi-Object Spectrograph (KMOS) the telescope’s 8.2-meter Very Large Telescope of the European Southern Observatory on Cerro Paranal , in Chile.

Thanks to the extreme sensitivity of the instrument, the researchers were able to infer the speed of rotation of the outer regions of the six galaxies. Data analysis showed that these speeds decrease with much more quickly within what happens in the local universe galaxies, suggesting that in these dark matter is not as dominant as in those nearby.



To open the video click on the image, good view from your Alessandro Brizzi.