Cosmological Feedbacks from the First Stars.

It is very natural for us in a clear night to raise the head and look at the starry sky. We are so used to such emotion that we hardly imagine a dark sky, where no shimmering light attracts our constantly changing attention. However, for how peculiar this might seem to us, there was a time when no stars were born yet and the universe resembled a vast, quiet (and somewhat boring) sea of inert hydrogen and helium gas. Darkness was everywhere, as the light produced by the Big Bang rapidly shifted out of the visible range and into the infrared. Such situation lasted for many million years (now we speculate about 200Myr). The study of these remote times is a relatively new area in cosmology. These epochs can still be compared to the Old Wild West territories which only brave pioneers have dared to explore. The gold mines containing precious information about the dawn of the universe, when the first luminous sources brightened up and their light unveiled the already ongoing formation of large numbers of pregalactic systems, are still not at reach of the yet most powerful experimental devices currently available to us. This situation is going to change soon, but at the moment theorists' predictions remain in the realm of sophisticated (and intellectually exciting) speculations. For how uncertain all this might be considered, there is a great deal of knowledge that can be gathered even under these unfavorable conditions, as witnessed by the impressive momentum gained by the field in the very recent years. Thus, as observations are slowly, but steadily filling the gap with theory, this school very suitably serves the scope of setting a common framework among theory and observation. The present Lectures aim at discussing the current understanding of the properties of first cosmic stars. These stars had a dramatic impact on the surrounding environment regulated by a complex network of physical processes to which we - somewhat ambiguously - usually refer to as feedback. Before the start, a short caveat on the suggested literature. It would be impossible to give credit to all the results and people whose efforts are constantly re-shaping the field in this brief essay. In fact we do not aim at giving a comprehensive view of all the aspects concerning the subject; for this we defer the reader to the most recent and technical reviews available: [4, 11, 15]. Instead, we hope that we will be able to outline the physics of the most relevant processes regulating the evolution of the first luminous sources and their effects. [ABSTRACT FROM AUTHOR]