2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8916Precise knowledge of the features of several X-ray sources from compact binary sources to galactic nuclei is gradually unveiling the physical parameters of relativistic neutron stars and black holes therein. Recent developments in theory, astrophysical models and experiments are reviewed.7 pages, 2 figures; submitted to Nuovo Cimento BAstrophysicstext