Physicists from the United States have proposed that the 220-petaelectronvolt neutrino detected by the KM3NeT detector could be the result of a primordial black hole exploding at the end of its lifespan. The model suggests that a small fraction of such objects could explain both the rare burst and the high-energy events previously observed by the IceCube observatory. The study was published in the journal Physical Review Letters.
The first ideas about primordial black holes emerged half a century ago. Stephen Hawking proposed their existence as candidates for dark matter. According to modern calculations, if they formed in the early universe from density fluctuations, some of them should now be living out their final moments, evaporating through the Hawking effect. During this process, the hole's temperature increases inversely proportional to its mass, and the final milliseconds of its life are accompanied by the emission of particles with energies comparable to the Planck energy.
Alexandra Klipfel and David Kaiser of the Massachusetts Institute of Technology calculated how many neutrinos with energies above petaelectronvolts could be produced by the explosion of such objects. They showed that for a mass of about 5 × 10 grams—corresponding to a lifetime equal to the age of the universe—the resulting evaporation is accompanied by the emission of about 10 neutrinos. The rate of such explosions, inferred from IceCube data, was 1,400 events per cubic parsec per year, consistent with upper limits from gamma-ray observations.
With these parameters, the probability that at least one similar explosion has occurred within 2,000 astronomical units of Earth since IceCube's launch in 2011 is about 7 percent—sufficient to explain the rare event KM3-230213A. According to the model, both observation series—IceCube and KM3NeT—could originate from the same population of primordial black holes with a characteristic mass of approximately 1017 grams.
The authors note that future neutrino detectors and gamma-ray observatories, including LHAASO, will be able to test this hypothesis by limiting the number of localized explosions to hundreds per cubic parsec per year. If these calculations are confirmed, rare, ultra-energetic neutrinos could be direct witnesses to the final moments of ancient black holes.
Scientists continue to find new uses for hypothetical primordial black holes. For example, physicists previously explained the formation of heavy elements in the Universe using primordial black holes.
