2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/166354This contribution discusses some of the main problems in high energy astrophysics, and the perspectives to solve them using different types of "messengers": cosmic rays, photons and neutrinosTalk given at the workshop "Neutrino Oscillations in Venice" (april 2008)Astrophysicstext