Russian physicists have calculated how much dark matter has been lost since the Big Bang, a discovery that explains the discrepancy between the cosmological parameters in the modern Universe and the Universe shortly after the Big Bang.

Using data from observations of various cosmological effects, the Russian researchers were able to give an estimate of the relative concentration of the decaying components of dark matter in the region 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 era. We are not currently able to say how quickly this unstable part decayed," said Igor Tkachev, Head of the Department of Experimental Physics at INR and a lecturer at MIPT's Department of Fundamental Interactions and Cosmology.

"Dark matter may still be disintegrating even now, although that would be a different and considerably more complex model."

The recombination era took place some 300,000 years after the Big Bang. It describes the period of time in which the early Universe cooled enough for electrons and protons to form and bond together into hydrogen atoms.

Tkachev said scientists have, 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.

Astronomers first suspected 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 didn't manifest itself in any way except for a gravitational effect and was given the name dark matter.

Data from the Planck space telescope shows the proportion of dark matter in the Universe is 26.8%. The rest consists of "ordinary" or baryonic matter (4.9%) and dark energy (68.3%).

The nature of dark matter remains unknown up until today, however. Dark matter's properties might help scientists solve the problem that arose after studying observations from the Planck telescope.

The Planck space telescope accurately measured the fluctuations in the temperature of the cosmic microwave background radiation, or the "echo" of the Big Bang. By measuring these fluctuations, researchers were able to calculate key cosmological parameters using observations of the Universe in the recombination era.

"However, it turned out that some of these parameters, namely the Hubble parameter, which describes the rate of expansion of the Universe, and also the parameter associated with the number of galaxies in clusters vary significantly with data that we obtain from observations of the modern Universe, by directly measuring the speed of expansion of galaxies and studying clusters," said Tkachev.

"This variance was significantly more than margins of error and systematic errors known to us. Therefore we are either dealing with some kind of unknown error, or the composition of the ancient Universe is considerably different to the modern Universe."

The discrepancy can be explained by the decaying dark matter (DDM) hypothesis, which states that in the early Universe there was more dark matter, but then part of it decayed.

The authors of the study were Tkachev, Dmitry Gorbunov and Anton Chudaykin from IRN, MIPT and NSU.

Tagsdark matter, Big Bang, Russian physicists, Igor Tkachev, Universe, planck space telescope, Dmitry Gorbunov, Anton Chudaykin