Researchers at the Space Research Institute (SRI), MIPT and the Institute of Astrophysics of the Max Planck Society have shown that the diffusion of the particles in the gas flowing into the center formed in the early universe galaxies, could affect the ratio between the content of hydrogen and helium within the first galaxies. This was reported in the received press release. According to the calculations of scientists, because of this phenomenon changes in the relative amount of helium can reach values comparable with the precision of modern theoretical predictions. This means that the observed abundance of helium and hydrogen can vary. The work is published in the Monthly Notices of the Royal Astronomical Society journal.
Scientists have been interested in learning how important it is to take into account the effect of diffusion in the era of the formation of the first stars and galaxies due to the fact that the accuracy of the direct measurement of the abundance of primary cells grows every year.
In order to describe the state of the universe at all stages of its development physicists use the so-called cosmological parameters. For example, the Hubble parameter that determines the rate of expansion of the universe, or the parameters that define the relationship between matter and dark energy. If physicists know the time-varying values of these parameters at all stages of evolution of the Universe, they will be able to look billions of years back or forward and create an accurate model of the universe.
Methods of calculation of cosmological parameters with high accuracy have been developed. One of them is a direct measurement of the abundance of the primary elements, it makes it possible to determine the so-called baryon-photon ratio in the universe, which enables to find the contribution of normal matter (baryons) to the full current energy density in the universe.
The modern theory of the universe states that in the first minutes after the Big Bang nucleosynthesis began the process that led to the unification of protons and neutrons in the nucleus of primary cells. The primary hydrogen gas along with mostly helium contained a small amount of deuterium and lithium. This epoch is particularly interesting for physicists, it is the earliest stage of evolution of the universe, and today we have reliable observations of it.
Physicists Pavel Medvedev, Sergei Sazonov and Marat Gilfanov suggested that ascribed to hydrogen amount of the primary helium could change in the course of evolution of the universe as a result of diffusion action of the gas forming the first galaxies.
In the process of formation of galaxies firstly dark matter is shrinking rapidly, then this zone begins to drain gas. We believe that diffusion is possible in this gas stream. It leads to the fact that particles of different masses are moving at unequal speeds. Lets assume that gas consists of hydrogen and helium. Helium is a heavier particle, so it will settle more quickly than hydrogen in the gravitational field of the galaxy formed. As a result, the resulting galaxy relative abundance of helium to hydrogen abundance is different from the value that is predicted by the theory of nucleosynthesis, - Sergey Sazonov of the Space Research Institute and MIPT commented.
The researchers examined the diffusion of particles in a gas in the process of the formation of galaxies at the early stages of the universe and considered what would be the effect caused by this change in the relative content of helium in galaxies of a given mass. It turned out that it could reach hundredths of a percent in the diffusion in the cold gas. If the gas in the Universe during the formation of the first galaxies (a few hundred million years after the Big Bang) has been warmed up to several thousand degrees, the diffusion could lead to a change in the relative amount of helium to tenths of a percent.
One of the reasons for gas heating could be a transfer of energy of the explosion of the first supernovae environment using cosmic rays.
This new mechanism for heating the universe was proposed by Sergey Sazonov and Rashid Sunyaev in previous work.
Primary helium is measured in the interstellar gas of galaxies close to us in areas where there are no stars. It is necessary that the observed substance is primary, rather than a product of thermonuclear burning of hydrogen in stars. Direct measurement of the abundance of primordial helium enables to limit the cosmological parameters and test the theory of primordial nucleosynthesis. Cosmological parameters, as mentioned above, set the state of the universe at any given time. Therefore, their determination with maximum accuracy is one of the main problems of cosmology.
The accuracy of predicting the abundance of helium equals to the change in values ??introduced by diffusion. In other words, the authors proposed a physical effect that can change the content of helium in galaxies within the measurement accuracy. Accordingly, more precise future prediction based on measured data should take into account such an effect.