The discovery of neutrinos revolutionized physics. Thanks to these elementary particles, born in the process of nuclear transformations, it was possible to explain where the energy of the Sun comes from and how long it has left to live. RIA Novosti talks about the features of solar neutrinos and why they should be studied.
Why does the sun shine
Physicists have guessed about the existence of a mysterious elementary particle with zero charge emitted during radioactive decay since the 1930s. Italian scientist Enrico Fermi called it a small neutron - neutrino. This (then still hypothetical) particle helped to understand the nature of the luminosity of the Sun.
According to calculations, each square centimeter of the Earth's surface receives two calories from the Sun per minute. Knowing the distance to the star, it was not difficult to determine the luminosity: 4 * 1033 erg. Where does it come from - this question has not been answered for a long time. If the sun, which is mainly composed of hydrogen, simply burned, it would not have existed for ten thousand years. Considering that the volume decreases during combustion, the Sun should, on the contrary, be heated by the forces of gravity. In this case, it would have extinguished in about thirty million years. And since it is more than four billion years old, it means that it has a constant source of energy.
Such a source at monstrous temperatures inside a star can be the reaction of helium fusion from two protons entering the hydrogen nucleus. In this case, a lot of thermal energy is released and one neutrino particle is formed. Based on its size, the Sun could burn for ten billion years before finally cooling down, turning into a red giant.
To be convinced of the validity of this hypothesis, it was necessary to register neutrinos born inside the Sun. Calculations showed that it would be difficult to do this, since the particle interacts very weakly with matter and has an amazing penetrating ability. When it is born, it does not react with anything else and reaches Earth in eight minutes. When the sun shines, every square centimeter of our skin is pierced by about a hundred billion neutrinos per second. But we do not notice this. Particle streams easily pass through planets, galaxies, star clusters. By the way, relic neutrinos born in the first seconds of the Big Bang are still flying in the Universe.
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Caught for poison, water and metal
Despite the inertness, neutrinos still sometimes collide with atoms of matter. There are only a few such events per day. If you shield the detector from photons, cosmic radiation, natural radioactivity, then the result of collisions can be registered. This is why neutrino traps are placed deep underground or in mountain tunnels.
The first method for registering solar neutrinos was proposed in 1946 by the Italian physicist Bruno Pontecorvo, who worked in Dubna near Moscow. He wrote a simple reaction of the interaction of a particle with a chlorine atom, resulting in the birth of radioactive argon. An installation of this type was built in the Homestake underground laboratory in the USA, where solar neutrinos were recorded for the first time in 1970. In 2002, physicist Raymond Davies, who received these results, was awarded the Nobel Prize.
Vadim Kuzmin from the Institute for Nuclear Research, Russian Academy of Sciences, invented a way to detect the passage of neutrinos through a gallium solution. As a result of the collision of particles with atoms of this element, radioactive germanium is formed. Since 1986, a detector based on this principle has been operating at the Baksan Neutrino Observatory (North Caucasus) as part of the SAGE joint experiment in the USA.
A year earlier, observations of neutrinos had begun at the Kamiokande facility in Japan, where the detector was water, which glowed blue when electrons were born. This is the so-called Cherenkov radiation.
Solar neutrinos are lost and found
When scientists from different countries have accumulated data on the number of reactions of neutrinos with matter, it turned out that they are two to three times less than the theory suggests. The problem of neutrino deficiency arose. To solve it, it was proposed to lower the temperature of the Sun and generally change ideas about it. It took three decades to find the answer, and instead of coming up with a new model of our star, physicists created a new theory of neutrinos.
It turned out that on the way from the star to the Earth, the particles are capable of reincarnating in their various modifications. This phenomenon was called neutrino oscillation. In 2015, the Nobel Prize was awarded for its confirmation, and experiments at the Baksan Neutrino Observatory played a decisive role. Now it is planned to build a universal detector there, registering all types of neutrinos and antineutrinos from all sources: the Sun, the center of the Galaxy, from the Earth's core.
If physicists initially studied neutrinos in order to better understand the Sun and the thermonuclear fusion taking place in it, now this fundamental particle has interested scientists in itself. It is known that the mass of neutrinos is very small, but it has not yet been calculated for sure. And this is important to understand the nature of the hidden mass of the Universe. The existence of a sterile neutrino is also suspected, interacting with matter only through gravity. Astronomers have high hopes for neutrino physics, since it allows them to look into the bowels of stars and black holes, to learn about the origin of space. The secrets of neutrinos continue to be comprehended in many observatories of the world, including those located in the waters of Lake Baikal and on the glacier of Antarctica.
Tatiana Pichugina
