Introduction

In this chapter, we look in a little more detail into some aspects of stellar evolution which will be important for studies of high energy astrophysical processes in our Galaxy and in extragalactic systems. For example, we need to know how far we can trust the theory of stellar structure and evolution; we need to know more details of the processes of nucleosynthesis in stars in order to understand the origin of the chemical composition of the interstellar gas and of the cosmic rays; we need to study what is known about the processes of mass loss from stars and the processes which can lead to the formation of dead stars; we need to investigate binary star systems in order to contrast their properties with those of X-ray binary systems containing neutron stars and black holes, and to discuss how such close binary stars can be formed. This survey is in no sense complete, and reference should be made to the texts recommended at the end of the book for more details.

The Sun as a star

Granted the outline of stellar evolution presented in Section 13.3, how well can the theory account for the properties of our own Sun? As by far the brightest star from our location in the Universe, it can be studied in much more detail than any other star, and is a benchmark for the theory of stellar structure and evolution. Until the last 20 years, the study of the Sun and the stars was largely confined to the interpretation of their surface properties.