Canadian physicists have shown that axion-like ultra-light dark matter can generate powerful ultraviolet radiation to quickly form supermassive black holes. Moreover, such formation can occur directly from cold gas, without the usual star formation phase. An article describing the work is posted in the arXiv.org repository.
According to modern observations, black holes with a mass of several billion solar masses already existed in the Universe about a billion years after the Big Bang. However, the mechanism of their formation still remains a mystery. Scientists assume that such objects could have appeared as a result of direct collapse. In this case, a massive gas cloud at the early stages of galaxy formation should be compressed into a black hole, bypassing the stage of star formation bursts. However, for this to happen, the molecular hydrogen in the cloud must not have time to cool the gas and cause it to break up into smaller parts. A large flow of ultraviolet photons, the source of which is currently the subject of scientific debate, could prevent the formation of molecular hydrogen.
Physicists Hao Jiao, Robert Brandenberger and Vahid Kamali from McGill University have proposed a mechanism for the formation of such photons using ultra-light dark matter. The scientists considered axion-like dark matter, which weakly, but still interacts with the electromagnetic field. In large halos of such matter, the field oscillates quite consistently, which generates a cascade of photons in the infrared range through the parametric resonance effect. Then these photons either move into the thermal spectrum, increasing the temperature of the gas, or, using a turbulent cascade, shift to ultraviolet energies sufficient to ionize hydrogen and suppress the formation of its molecules. The scientists' calculations showed that even with a very weak connection between the axion and light, such a model is capable of providing the necessary level of ultraviolet radiation for direct collapse and the formation of heavy black holes with a mass of about one hundred thousand solar masses.
The authors of the paper note that, unlike traditional scenarios, neither the radiation of hot stars nor the specific structure of the nascent galaxy are required here. Consequently, direct collapse could have begun even before the era of active star formation, which naturally explains the presence of supermassive black holes at high redshifts.
It is worth noting that at the moment it has not been possible to register axions, but physicists continue to search for them.