At the center of many galaxies lurks a black hole — an object predicted by solutions to the equations of Karl Schwarzschild. Around it stretches a scorching corona — a region of tenuous plasma heated to billions of degrees. By analogy with the solar corona, but incomparably hotter and denser, it serves as a natural particle accelerator. It is here, in this extreme cauldron, that neutrinos are born — ghostly particles whose existence was postulated by Wolfgang Pauli to save the law of conservation of energy. Neutrinos barely interact with matter: to stop even half of them, you would need a lead wall a light-year thick — the distance light travels in a year. This analogy simplifies reality but vividly illustrates their astonishing penetrating power.

Protons, the nuclei of hydrogen atoms captured from the surrounding gas, are accelerated to near-light speeds by the corona's powerful magnetic fields. Colliding with the intense X-ray radiation emitted by the same corona, they undergo photonuclear reactions and produce neutrinos. Previously, it was thought that the main source of such particles was relativistic plasma jets — jets ejected by active galaxies. However, data from the Antarctic neutrino observatory IceCube, a giant detector frozen into the ice, refuted this hypothesis. Analysis of events showed that the main suppliers of neutrinos turned out to be quiet galaxies without jets, where only the corona emits. Their contribution explains almost the entire observed neutrino flux up to energies of a petaelectronvolt (10¹⁵ eV).

Only for particles with record, even higher energies is the coronal mechanism alone insufficient — then galaxies with relativistic jets take the stage. Thus, combining direct observations of 'ghosts' with theoretical models, we step by step reconstruct the full picture of their origin.