2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34457We derive the delay in travel time of photons due to the spin of a body both inside a rotating shell and outside a rotating body. We then show that this time delay by the spin of an astrophysical object might be detected in different images of the same source by gravitational lensing; it might be relevant in the determination of the Hubble constant using accurate measurements of the time delay between the images of some gravitational lens systems. The measurement of the spin-time-delay might also provide a further observable to estimate the dark matter content in galaxies, clusters, or super-clusters of galaxies.Submitted to Physical Review Letters: 8 April 2002. Resubmitted, revised: 31 July 2002; 31 December 2002General Relativity and Quantum Cosmologytext