2018-04-29 12:44:42
In 1984, galaxies containing only about 1% of the stars of a classical galaxy were discovered, which is why they are known as ultra-diffuse galaxies. Obviously, ultra-diffuse galaxies must form in areas of the universe where, for some reason, ordinary matter is not as abundant as in the regions where classical galaxies form. However, since dark matter, if it existed, would be about five times more abundant than ordinary matter, it should also be present in ultra-diffuse galaxies, although it might also be found in less than normal abundance.
In an attempt to estimate whether dark matter is in the same proportion as classical matter in ultra-diffuse galaxies, researchers from Yale University are analyzing the stellar motion dynamics of one of these galaxies, called NGC1052-DF2, discovered in 2015 and located at about 65 million light-years. After analyzing the movement of the stars that make up this galaxy, the scientists conclude, to their great surprise, that this can be completely explained by the gravity generated by the classical matter contained in that galaxy. This would therefore lack dark matter or, if it does, it would do so in a much smaller proportion than normal.
These facts leave without explanation how and why a galaxy could have formed without the help of dark matter. Nor is it known how this, being supposedly much more abundant, has been excluded from a zone of space from which the classical matter that originated the galaxy has not been excluded. However, paradoxically, the existence of this galaxy lacking dark matter confirms that the rest of the galaxies must possess it, that is, it confirms that it does, in fact, exist, since it is much more improbable that gravity acts in different ways. in specific areas of the universe and stop doing it just a little further in astronomical terms, which would be necessary to explain the existence of this ultra-diffuse galaxy without dark matter.
Thus, the absence of dark matter in this specific case is evidence of its existence for the rest of the observed cases. Astronomers continue to search for new ultra-diffuse galaxies to analyze and confirm whether they also lack dark matter. We will have to wait, but little by little, science will always end the darkness.
Referencia: Pieter van Dokkum, et al. A galaxy lacking dark matter. Nature volume 555, pages 629–632 (29 March 2018). doi:10.1038/nature25767
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