Compact Dark Objects and Gravitational Microlensing towards the Large Magellanic Cloud

摘要

Most of the matter in the galaxies is invisible to a direct observations. This dark matter is distributed in space differently than the stars and the gas, forming very vast and massive structures around galaxies, more spherical than disklike, called haloes. The composition of these haloes is unknown. It may comprise a mixture of exotic, hypothetical elementary particles and baryonic material, which can exist in several dark form, including planets, brown dwarfs, ancient degenerate dwarf stars, neutron stars and black holes, collectively known as massive compact halo objects (MACHOs). When a MACHO in the halo of our galaxy is sufficiently close to the line of sight between us and a more distant star, the light emitted from this source star suffers a gravitational deflection, according to the theory of General Relativity. The MACHO, acting as a gravitational lens, produces a microlensing effect, that is a potentially huge magnification of the source light. In this way, the MACHOs could be detected indirectly by their gravitational field. We analyzed the features of microlensing events found looking towards a Milky Way satellite, the Large Magellanic Cloud.