The amount of dark matter in the Universe has decreased by about 2-5%, which may explain the discrepancies in the values of some important cosmological parameters during the Big Bang and today, Russian cosmologists say in an article published in the journal Physical Review D.
“Let's imagine that dark matter consists of several components, like ordinary matter. And one component consists of unstable particles, whose lifetime is quite long: in the epoch of hydrogen formation, hundreds of thousands of years after the Big Bang, they are still in the Universe, and today they have already disappeared, decaying into neutrinos or hypothetical relativistic particles. Then the amount of dark matter in the past and today will be different,”said Dmitry Gorbunov from the Moscow Phystech, quoted by the press service of the university.
Dark matter is a hypothetical substance that manifests itself exclusively through gravitational interaction with galaxies, introducing distortions in their movement. Particles of dark matter do not interact with any types of electromagnetic radiation, and therefore cannot be detected during direct observations. Dark matter accounts for about 26% of the mass of the Universe, while "ordinary" matter accounts for only about 4.8% of its mass - everything else falls on no less mysterious dark energy.
Observations of the distribution of dark matter in the closest and distant corners of the universe, carried out using ground-based telescopes and the Planck probe, recently revealed a strange thing - it turned out that the expansion rate of the Universe, and some properties of the "echo" of the Big Bang in the distant past and today are markedly different. For example, today galaxies fly apart from each other much faster than it follows from the results of the analysis of the relic radiation.
Gorbunov and his colleagues found a possible reason for this.
A year ago, one of the authors of the article, Academician Igor Tkachev from the Institute of Nuclear Physics of the Russian Academy of Sciences in Moscow, formulated the theory of so-called decaying dark matter (DDM), in which, in contrast to the generally accepted theory of "cold dark matter" (CDM), part or all of it particles are unstable. These particles, as suggested by Tkachev and his associates, should decay rather rarely, but in noticeable quantities in order to generate deviations between the young and modern Universe.
In their new work, Tkachev, Gorbunov and their colleague Anton Chudaykin tried to calculate how much dark matter had to decay using data collected by Planck and other observatories that studied the cosmic microwave background radiation and the first galaxies in the universe.
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As their calculations showed, the decay of dark matter can really explain why the results of observations of this substance with the "Planck" do not correspond to the data of observations of the nearest clusters of galaxies.
Interestingly, this requires the decay of a relatively small amount of dark matter - from 2.5 to 5% of its total mass, the amount of which is almost independent of what fundamental properties the universe should have. Now, as scientists explain, all this matter has decayed, and the rest of the dark matter, stable in nature, behaves as described by the CDM theory. On the other hand, it is also possible that it continues to disintegrate.
“This means that in today's Universe there is 5% less dark matter than it was during the formation of the first molecules of hydrogen and helium after the birth of the Universe. Now we cannot say how quickly this unstable part disintegrated, it is possible that dark matter continues to decay even now, although this is already another much more complex model,”concludes Tkachev.
