Summary Black holes are arguably the most extraordinary physical objects we know in the universe. Despite our thorough knowledge of black hole dynamics and our ability to solve Einstein's equations in situations of ever increasing complexity, the deeper implications of the very existence of black holes for our understanding of space, time, causality, information, and many other things remain poorly understood. In this paper I survey some of these problems. If something is going to be clear from my presentation, I hope it will be that around black holes science and metaphysics become more interwoven than anywhere else in the universe.

Resumen Los agujeros negros son posiblemente los objetos físicos más extraordinarios que conocemos en el universo. A pesar de nuestro gran conocimiento de su dinámica y de nuestra capacidad para resolver las ecuaciones de Einstein en situaciones de creciente complejidad, seguimos teniendo un entendimiento limitado de las implicaciones más profundas de la existencia de los agujeros negros para nuestra comprensión del espacio, el tiempo, la causalidad, la información y muchas otras cosas. Aquí examino algunos de estos problemas. Espero que quede claro a partir de mi presentación que alrededor de los agujeros negros la ciencia y la metafísica se entrelazan más que en cualquier otro lugar del universo.

A hadronic model for gamma-ray production in microquasars is presented. Microquasars are galactic binary systems with jets, which have, presumably, hadronic components. We consider a microquasar formed by a neutron star that accretes matter from the equatorial wind of a Be primary star. The collision between the jet, emitted by the compact object, and the dense equatorial disk of the companion massive star is responsible for the gamma-ray production. Gamma-rays result from the decay of neutral pions produced in relativistic pp interactions arising from this collision all along the orbit. Assuming a simple, positional independent set of parameters, our calculations are consistent with a peak of gamma-ray flux at the periastron passage with a secondary maximum near apastron. Under this assumption, gamma-ray signals would be in contrast with the radio/X-ray outbursts which peak clearly after periastron. We finally calculate the opacity of the ambient photon field to the propagation of the gamma-rays. The spectral energy distribution appears strongly attenuated in a wide band (50 GeV - 50 TeV) due to local absorption. These spectral features should be detectable by an instrument like MAGIC through exposures integrated along several periastron passages.