The first observations of the Chinese orbiting observatory DAMPE, designed to search for dark matter, speak in favor of the fact that dark matter can actually decay in the vicinity of the Earth's orbit and in the center of the Galaxy, scientists say in an article in the journal Nature.
“This 'cutoff' in the spectrum of cosmic rays, which we discovered, may indicate the existence of dark matter. On the other hand, it could have originated from some other source of these particles. More data is needed to answer this question, and we still expect DAMPE to operate for at least another 5 years,”said Chang Jin of the Zijinshan Observatory in Nanjing, China.
Dark skies
For a long time, scientists believed that the universe consists of the matter that we see, and which forms the basis of all stars, black holes, nebulae, dust clusters and planets. But the first observations of the speed of movement of stars in nearby galaxies showed that the stars on their outskirts move in them at an impossibly high speed, which was about 10 times higher than calculations based on the masses of all the stars in them showed.
The reason for this, according to scientists today, was the so-called dark matter - a mysterious substance, which accounts for about 75% of the mass of matter in the Universe. Typically, each galaxy has about 8-10 times more dark matter than its visible cousin, and this dark matter holds the stars in place and prevents them from scattering.
Today, almost all scientists are convinced of the existence of dark matter, but its properties, in addition to its obvious gravitational influence on galaxies and galaxy clusters, remain a mystery and a subject of controversy among astrophysicists and cosmologists. For a long time, scientists have assumed that it is composed of superheavy and "cold" particles - "wimps" that do not manifest themselves in any way, except by attracting visible clusters of matter.
The first potential traces of dark matter were found in 2008 by the Russian satellite Resurs-DK1, whose PAMELA detector detected traces of an unusually large number of antimatter particles in Earth's orbit, which, scientists have suggested, could be generated by the decays of this mysterious substance.
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Later, these data were confirmed by the AMS-02 detector on board the ISS, however, many astrophysicists disagree with this idea and believe that in fact this antimatter is of less exotic origin - it could have been generated by pulsars or some other distant sources of cosmic rays of high energies.
This year, the "pulsar" theory was called into question after the publication of data collected by the high-altitude HAWC telescope, which observes the universe in the gamma range. This revived the interest of physicists in "exotic" explanations for this strange anomaly in Earth's orbit.
Cosmological riddles
The DAMPE Space Telescope, launched by China into Earth's orbit in December 2015, has tested these assumptions on the other side by observing ultra-high-energy cosmic rays of unknown origin, originating in the center of our Galaxy and other star clusters.
This radiation, according to some cosmologists today, can also arise as a result of the decays of dark matter at those points where it accumulates especially a lot. If this is the case, then the cosmic rays emanating from the center of the Galaxy will have a special energy spectrum - the number of particles will initially change relatively slowly as the energy increases, but upon reaching a certain point, it will sharply sink down.
The first hints of the existence of this "cliff", as noted by Jin, were found during observations on AMS-02, but this detector could not track ultra-high-energy particles that DAMPE can "see", and data from ground-based telescopes were not sufficient accurate in order to say for sure.
According to Chinese physicists, the data collected by DAMPE during its first cycle of operation from December 2015 to June 2017 is the first definitive evidence that this "cliff" really exists and that it is located exactly where it should be in accordance with with theory predictions.
Over the next five years, Jin and his colleagues hope, DAMPE will collect data on another 10 billion cosmic rays, which will allow scientists to reduce measurement errors and finally prove that this anomaly exists.
It is not yet clear whether it arose as a result of the decays of dark matter or some less exotic processes. Physicists hope that observing ultra-high-energy beams, whose energies exceed 10 TeV, will help us understand whether they originated during the decays of dark matter or were generated by pulsars or supernova remnants.