Matter at High Densities in Astrophysics. Compact Stars and the Equation of State

Abstract

This monograph is a Festschrift to honour the 100th birthday of Friedrich Hund whose name is well known for his contributions in the early days of quantum theory and during its subsequent development. In 1936, he wrote a review article (which is reprinted here, together with an English translation) about the nature and properties of matter under extreme conditions, relating this to circumstances inside stars and planets. At that time, white dwarfs had been observed and identified as objects supported by electron degeneracy pressure and neutron stars had also been predicted theoretically, although it was not until very much later, of course, that pulsars were observed and identified with them. Reading his article today, one is impressed by the methodical way in which the new and exciting developments in physics of that time were assembled together with pre-existing knowledge in order to build up this picture of the interiors of astronomical objects. The main part of the book is the combined work of a group of authors associated with Hund and deals with interrelated topics which follow on from his 1936 article, presenting modern developments. It has the form of a monograph but the flavour is more that of a summer school with the changes of subject matter and the differing approaches and styles providing a pleasing unevenness which seems very appropriate for a volume of this kind. After a brief historical introduction and a short chapter outlining the basic ideas of stellar structure, the rest of the book is divided into three parts dealing respectively with: the equation of state of matter under conditions appropriate for neutron stars; the construction of numerical models for non-rotating and rotating neutron stars and the study and use of seismology for finding out about the internal structure of planets, ordinary stars and compact stars. The chapter on the equation of state is a detailed technical presentation aimed at physicists familiar with the ideas of quantum many-body theory. Indeed, it may well appeal particularly to people from this background who normally work on other applications. It is a `standard' presentation in the sense that more exotic ideas such as those leading to the strange-star and Q-star models are not discussed, perhaps a pity in view of the amount of literature devoted to these, although one can understand why. Whereas this chapter is a general review, the one on constructing neutron-star models concentrates mainly on presenting (interesting) work by one of the authors and his colleagues. I liked their ray-traced pictures of how rotating neutron stars would appear to an external observer. The study of seismic modes in stars is a fascinating one which is progressively revealing more and more about the internal structures. The chapter dealing with this is again a general review. This is not a systematic general introductory book from which to learn the basics about compact stars ( Black Holes, White Dwarfs and Neutron Stars by Shapiro and Teukolsky is still unrivalled for that) but it is a stimulating read for physicists interested in these questions and a fitting tribute to Friedrich Hund.