Chandrasekhar’s book An Introduction to the Study of Stellar Structure

Abstract

For me, and for many astrophysicists of my generation, Chandrasekhar’s book An Introduction to the Study of Stellar Structure was very important. I could not have done my PhD (1962–1965) without it. Much more recently (1998) I realized that I could not have written my lecture course on thermodynamics and statistical mechanics without much of it, particularly the first chapter. I shall present anecdotal evidence that the influence of his discussion on the second law of thermodynamics has been important not just for astrophysics but for a much wider range of physics.

Chandrasekhar’s discussion of polytropes was masterly. Even today polytropes play an important role as an aid for understanding stellar structure. I believe that to the list of analytic solutions of the polytrope only one more has to be added: a curious n = 5 model of Srivastava (1962).

Stellar structure is nowadays a very computationally intensive subject. I shall illustrate this with a couple of topics from my experience with Djehuty, a supercomputer code for modelling stars in 3D. Nevertheless it remains true, I believe, that analytical mathematical entities like polytropes are fundamental as aids for understanding what the computers churn out.

How close are we to seeing a book with the title ‘The Last Word on the Study of Stellar Structure’? Not very, although much has been learned in 70 years. I shall discuss a few of the aspects of stellar evolution that are problematic today.

I shall discuss a couple of aspects where I believe analysis of ‘piecewise polytropic’ structures sheds light on the question ‘Why do stars become red giants?’