Modern astronomy has stretched its domains of exploration tremendously. Not only objects at very large distances and very old states of the Universe can be examined, but also all kinds of radiations and phenomena are now accessible. Astronomers constantly move from considerations about very - luted to very dense systems. Hot and energetic systems, being the easiest to observe, have attracted a lot of attention. However the cold and low energetic states have been so- what neglected, either because being harder to observe they appear unexc- ing, or because being less well known they tend to be...