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Astronomers first suspected that there was a large proportion of "hidden mass" in the Universe back in the 1930s, when Fritz Zwicky discovered "peculiarities" in a cluster of galaxies in the constellation Coma Berenices - the galaxies moved as if they were under the effect of gravity from an unseen source. This hidden mass that does not manifest itself in any way, except for a gravitational effect, was given the name dark matter. According to data from the Planck space telescope, the proportion of dark matter in the Universe is 26.8%, the rest is "ordinary" matter (4.9%) and dark energy (68.3%). Scientists from MIPT, the Institute for Nuclear Research (INR) of the Russian Academy of Sciences, and Novosibirsk State University (NSU) have discovered that the proportion of unstable particles in the composition of dark matter in the days immediately after the Big Bang was no more than 2%-5%. Their study has been published in Physical Review D.

"The discrepancy between the cosmological parameters in the modern Universe and the Universe shortly after the Big Bang can be explained by the fact that the proportion of dark matter has decreased. We have now, for the first time, been able to calculate how much dark matter could have been lost and what the corresponding size of the unstable component would be," says a co-author of the study academician Igor Tkachev, Head of the Department of Experimental Physics at INR and a lecturer at MIPT's Department of Fundamental Interactions and Cosmology.

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