In this article, we summarise several of the most well-known astrophysical scenarios, and offer a brief description of what we currently know about them.
We see the sky and admire its regularity and stability, its apparent immutability. We have always done so; it does not come as a surprise, since humans have always been startled by any change in the sky, associating it with omens or the mood swings of gods. At that time, they might call these changes «new stars», even if they were, for example, a supernova explosion, as in the case of Tycho’s supernova in the sixteenth century.