2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/141791We will briefly discuss the importance of sensitive X-ray observations above 10 keV for a better understanding of the physical mechanisms associated to the Supermassive Black Hole primary emission and to the cosmological evolution of the most obscured Active Galactic Nuclei.6 pages, 5 figures, to appear in proceedings of "Simbol-X: the hard X-ray Universe in focus", held in Bologna (Italy), May 14-16, 2007Astrophysicstext