Mysterious fast radio flares, about the nature of which scientists have been arguing for a decade, can arise from the collision of large clusters of dark matter with black holes, according to the online magazine New Scientist.
“If a large number of clusters of axionic dark matter are present in the centers of galaxies, then such 'dark stars' should often collide with the accretion disk of a supermassive black hole. The powerful magnetic field of the disk should cause some of the axions to disintegrate, and give rise to a flash that reaches us in the form of a fast radio burst,”says Aiichi Iwazaki, an astronomer at Nisogakusha University in Tokyo, Japan.
For the first time, astronomers started talking about the existence of mysterious bursts of radio emission (fast radio-burst, FRB) in 2007, when they were accidentally discovered during observations of radio pulsars using the Parks telescope (Australia).
In subsequent years, scientists managed to find traces of nine more such bursts, a comparison of which showed that they can be of artificial origin and even potentially be signals of extraterrestrial civilizations due to the inexplicable periodicity in their structure.
Last spring, scientists discovered that the source of one of these FRB flares was an elliptical galaxy located 6 billion light years from the Milky Way. This led them to conclude that such bursts are born during the merger of neutron stars or other compact objects that turn into a black hole. Subsequently, astrophysicists discovered that FRB flares were repeated, which put these theories into question.
The unusual properties of these radio bursts, which do not allow them to be associated with either supernova explosions or mergers of black holes or pulsars, as Iwazaki notes, made him think about more exotic versions of the birth of such "alien signals."
All FRB flares known to astronomers, according to the astronomer, occurred in the centers of distant galaxies, and their most likely source is most likely supermassive black holes at their centers. What could cause them to generate such short and bright flashes, visible only in the radio range?
As Iwazaki's calculations show, flares of similar length, power and frequency can cause exotic "dark stars" - clusters of dark matter particles about 94 kilometers in diameter that inhabit the central part of galaxies. Such structures, as suggested by the Japanese astronomer, should not consist of classical superheavy particles of dark matter, the so-called "wimps", which do not interact with visible matter in any way, but of axions, their ultra-light analogs, similar in properties to neutrinos.
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According to the scientist, axions must interact with the strongest magnetic fields that exist in the so-called accretion disk - a "donut" of hot matter surrounding the black hole. Colliding with it, part of the axions in the "dark star" will decay into photons and generate powerful electric fields. These fields will accelerate the electrons present in the donut and cause them to produce beams of high-energy photons, whose physical properties will almost perfectly match what FRB flares look like.
This mechanism of the birth of "alien signals", according to Iwazaki, explains all their oddities, including the fact that their sources remain invisible to us in the ultraviolet and X-ray ranges, as well as why they are repeated, but at the same time are not periodic like radio signals from pulsars. On the other hand, scientists have not yet found any traces of the existence of axions, and, most likely, the source of FRB flares is some other cosmic phenomenon with a less exotic nature.
