Scientists have proposed a method for indirect detection of neutrinos originating in the first seconds of the universe

The Planck Space Observatory and the MFI map made with its help

American scientists from the University of California have proposed a new way to indirectly observe the earliest neutrinos originating in the first seconds of the existence of the Universe. According to their calculations, these neutrinos had a characteristic effect on cosmic microwave background radiation (MFI) and the distribution of matter, from which galaxies then formed.

The first moments of the Big Bang were very hot and active - so hot that even atoms could not exist in such conditions. In parallel with the expansion of the Universe, the formation of particles and the separation of four fundamental interactions took place. And then hadrons began to appear. At some point, the substance became transparent to neutrinos, which were able to move fairly freely without colliding with the rest of the substance.

All this took no more than 2 seconds - and then for another 400,000 years, light could not break through matter, so we will not see photons from this time period. But neutrinos, very weakly interacting with the rest of the substance, we could catch - if it were not so difficult to do.

But precisely because neutrinos interact weakly with other particles, even modern neutrino detectors like IceCube or the Dubna deep-sea neutrino telescope are capable of catching a very small number of these particles, especially those that originated at the beginning of the Universe - their energy is too low.

By analogy with microwave background radiation, scientists are talking about neutrino background radiation (NFI). Its temperature, which decreased with the expansion and cooling of the universe, is slightly less than that of microwave radiation, and amounts to 1.9 ° C.

Scientists have already compiled a map of the microwave radiation of the sky - but the NFI map has not yet been compiled, since it is not possible to directly capture the necessary neutrinos. But scientists from the University of California did not propose to capture the neutrinos themselves, but to record the consequences of their existence.

While matter was in the form of a hydrogen-helium plasma for 400 thousand years, neutrinos were already plowing the expanses of the Universe at a speed close to light. This speed exceeded the speed of sound in the plasma - therefore, sound waves generated by fast neutrinos should have propagated in it. Sound waves led to fluctuations in the density of primary matter, which can be measured.

These fluctuations led both to inhomogeneous distributions of matter, from which celestial objects were then formed, and to inhomogeneities of microwave background radiation, at which temperature variations are present in it.

The authors calculated how the MFI picture should theoretically look in the presence of fluctuations caused by neutrinos, and in the absence of such, while for variety they took options with different numbers of types of neutrinos. It turned out that the calculations coincide with the known pattern of radiation distribution when just three neutrino flavors are involved in the model - that is, the theory coincides with reality.

Researchers argue that although the effect of neutrinos on MFIs is small, it is not only palpable, but also quite characteristic. Another candidate instead of neutrinos could be an unknown form of dark matter, the particles of which would move at a speed around the light - which is unlikely.