"Let's imagine that dark matter consists of several components, as in plain material (protons, electrons, neutrons, neutrinos, photons). And one component consists of unstable particles with one quite long life: in the era of formation of hydrogen for hundreds of thousands of years after the big bang they are still in the universe, but for thousands of years they have disappeared due to neutrinos or hypothetical relativistic particles.
" the amount of dark matter in the aging of hydrogen formation and today being different, "said Dmitry Gorbunov at his Moscow Institute of Physics and Technology.
Astronomers first believed that there was a large part of" hidden mass "in the universe back in the 1930s when Fritz Zwicky discovered "special" in a cluster of galaxies in the constellation Coma Berenices – the galaxies moved as if they were under the effect of gravity from an invisible source. e mass that does not manifest itself in any way, except for a gravitational effect, was named dark matter. According to data from the Planck space telescope, the proportion of dark matter in the universe is 26.8%, the rest is "plain" material (4.9%) and dark energy (68.3%).
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In December 2016, MIPT researchers from the Institute of Nuclear Research (INR) from the Russian Academy of Sciences and Novosibirsk State University (NSU) discovered that the proportion of unstable particles in the composition of dark matter in The days immediately after the Big Bang were no more than 2% -5%.
"The discrepancy between the cosmological parameters of the modern universe and the universe shortly after the Big Bang can be explained by the fact that the proportion of dark matter has fallen. We have now for the first time been able to calculate how much dark material that could have been lost and what the corresponding size of the unstable component would be, "says a co-author of study academician Igor Tkachev, head of experimental physics at INR and a lecturer at MIPT's basic interactions and cosmology department.
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The nature of the dark matter remains unknown, but its properties could potentially help scientists solve the problem that arose after studying observations from the Planck telescope. This device accurately measured the fluctuations in the temperature of the cosmic microwave background radiation – "Big-Bang" "echo". By measuring these fluctuations, the researchers were able to calculate key cosmological parameters by observing the universe during the recombination period – about 300,000 years after the big bang.
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"It turned out, however, that some of these parameters, namely the Hubble parameter describing the expansion rate of the universe and also the parameter associated with the number of galaxies in clusters, vary considerably with data which We derive from observations of the modern universe, by directly measuring the rate of expansion of galaxies and studying clusters, which was considerably more than error margins and systematic errors we knew, so we either deal with some kind of unknown error, or the composition of the ancient universe is significantly different from the modern universe, says Tkachev.
The inconsistency can be explained by the overdue dark matter (DDM) hypothesis, which states in the early universe that there was more dark matter, but then became part of the past due.
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The authors of the study, Igor Tkachev, lead author Gorbunov and Anton Chudaykin analyzed Planck data and compared them to the DDM model and standard MCDM (Lambda-Cold Dark Matter) model with stable dark matter. The comparison showed that the DDM model is more consistent with the observation data. The researchers, however, found that the effect of gravitational lensing (distortion of cosmic microwave background radiation with a gravitational field) greatly limits the proportion of decaying dark matter in the DDM model.
Using data from observations of various cosmological effects, researchers were able to provide an estimate of the relative concentration of the decayed components in dark matter in the range of 2% to 5%.
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"This means that in today's universe there is 5% less dark matter than in the recombination time. We cannot at the moment say how quickly this unstable part falls due; the dark matter can still becoming disintegrating even now, though it would be a different and significantly more complex model, "says Tkachev.
The Daily Galaxy through Moscow Department of Physics and Technology
Picture at the top of the page: Early days: the artist's impression of stars formed by primordial hydrogen gas. (Courtesy: E R Fuller / National Science Foundation)