ABSTRACT
This chapter explains a closer look at the matter fluid, examines the contribution from different astrophysical components, and discusses how it is distributed in the universe and confirms in an independent direct way the result. The effects of the additional intergalactic dark matter component can be inferred from the motion of the galaxies in the clusters of galaxies. A minimal astrophysical explanation of dark matter is that it is made of faint astrophysical objects. There is, in addition, another known component of matter that cannot strictly speaking be included in the baryonic budget: black holes. A possibility is that the dark matter component might be explained in terms of a faint baryonic matter component, such as brown dwarfs and giant planets, jointly with a population of black holes. In gravitational microlensing, as opposed to strong and weak lensing, the shape of a source object is not deformed by the gravitational lens, but its brightness is temporarily changed.
