Canadian physicists have demonstrated that axion-like ultralight dark matter can generate powerful ultraviolet radiation to rapidly form supermassive black holes. Moreover, this formation can occur directly from cold gas, without the usual star formation phase. A paper describing the work has been posted on the arXiv.org repository.
According to modern observations, black holes with masses several billion times greater than those of the Sun already existed in the Universe approximately a billion years after the Big Bang. However, the mechanism of their formation remains a mystery. Scientists suggest that such objects could have arisen through direct collapse. In this case, a massive cloud of gas in the early stages of galaxy formation should have collapsed into a black hole, bypassing the starburst stage. However, for this to occur, the molecular hydrogen in the cloud must not have had time to cool the gas and cause it to fragment into smaller particles. A large flux of ultraviolet photons, the source of which remains a subject of scientific debate, could have prevented the formation of molecular hydrogen.
Physicists Hao Jiao, Robert Brandenberger, and Vahid Kamali from McGill University proposed a mechanism for the production of such photons using ultralight dark matter. The scientists considered axion-like dark matter, which weakly yet still interacts with the electromagnetic field. In large halos of such matter, the field oscillates quite consistently, generating a cascade of infrared photons through parametric resonance. These photons then either transition to the thermal spectrum, increasing the gas temperature, or, via 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 very weak axion-light coupling, this model is capable of generating the necessary level of ultraviolet radiation for direct collapse and the formation of heavy black holes with masses approximately one hundred thousand times that of the Sun.
The authors of the paper note that, unlike traditional scenarios, neither radiation from 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 axions have not yet been detected, but physicists continue to search for them.
