2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4699In the past five years observations with the Rossi X-ray Timing Explorer have revealed fast quasi-periodic oscillations in the X-ray flux of about 20 X-ray binaries. Thought to originate close to the surface of a neutron star, these oscillations provide unique information about the strong gravitational field in which they are produced.2 pages, no figures; to appear in the Proceedings of the 9th Marcel Grossman Meeting, eds., Vahe Gurzadyan, Robert Jantzen and Remo Ruffini, World ScientificAstrophysicstext