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Cosmology

The Tapestry of Modern Astrophysics by Steven N. Shore (Wiley-Interscience) This is a large book about a very big subject. The scope of modern astrophysics is, quite literally, the whole cosmos and everything in it.

The order of the topics is dictated by necessity. Astrophysics requires remote sensing. You need basic physical concepts‑ gravitation, thermodynamics, statistical mechanics, and radiative processes‑in order to understand how the bodies you are studying are structured. Nuclear physics, hydrodynamics, plasma processes and magnetohydrodynamics, and relativity play essential parts in the development of models. Increasingly, areas that have been thought to be separate in the curriculum come together in a beautiful cross‑disciplinary synthesis.

Chapter 1 begins with the basic physical processes common to all cosmic bodies, those involving gravitation, thermodynamics, and the gas laws. My aim is to show the similarity of many of the methods that are used to tackle what may otherwise appear to be very different problems. For instance, rather than postpone the discussion of stellar statistical dynamics to the chapter on galaxies, it is introduced here as an application of statistical mechanics to gravitational interactions in a gas of stars. A special feature of this first chapter is an appendix that provides an overview of general relativity, since this is needed for subsequent discussions of black holes in binary systems and active galactic nuclei, not to mention cosmology.

Chapter 2 reviews some of the general aspects of observations. These include calibration, instrumentation, and image formation and reconstruction with the goal of acquainting you with the idea that no astronomical observation is entirely "theory‑fine," and that much of the information provided by observations must be recovered from the data by manipulation.

Chapter 3 deals with radiative transfer, mainly in the context of stellar atmospheres, but also includes material theory of line formation that will be important in Chapter 6 on the interstellar medium and Chapter 8 on cosmology. It also introduces concepts of spectral classification and discusses stellar atmospheres in a general way in order to describe the basis for analysis of stellar surface properties.

Chapter 4 deals with stellar structure, energy sources, evolution, and nucleosynthesis. A particular emphasis here is on pulsating stars as an example of a ubiquitous instability in stars. You will also find an appendix that briefly presents some basic: dynamo theory, for which there are broad astrophysical applications.

Chapter 5 presents an intermezzo on binary stars emphasizing processes that take place when tides limit the radial growth of stars. The chapter also provides an introduction to accretion disks and related phenomena. My justification for treating these objects in a separate chapter is that they present many phenomena that combine the material of the preceding chapters and also set the stage for discussions of accretion and disk formation that are needed for understanding galactic nuclei.

Chapter 6 covers the interstellar medium (ISM). It returns to radiative processes, this time treating the ISM as the ultimate example of a radiating gas in NLTE. Since some of the most spectacular examples of gas dynamics, shocks of all varieties, occur in the ISM, this chapter also introduces ideas about shocks and similarity solutions and reviews some features of turbulence.

Chapter 7 treats the Milky Way as a stellar system and as the prototype for the study of extragalactic systems. I have chosen to combine this discussion with a review of the properties of galaxies of various types in order to emphasize that our understanding of our own stellar system is informed by the study of external galaxies and vice versa. This chapter also covers radio galaxies, clusters of galaxies, and active galaxies.

Finally, in Chapter 8, we come to cosmology, where we begin with a discussion of the observational constraints and, in Weinberg's phrase, cosmography, and then go on to discuss the formation of structure and galaxies within the context of solutions of the field equations for different equations of state and scenarios for the earliest epochs of the Big Bang.

The coverage is slanted heavily toward stellar and interstellar processes. For this, I make no apologies. You can't understand galaxies without a detailed examination of their constituents. While with each successive step in the distance scale the questions become, in a sense, bigger, our loss of resolution means our inferences become more tentative and this loss of information at each step compounds our ignorance of the governing processes. In teaching science, a top‑down view may be magisterial but it is often misleading. In dealing with astrophysics it is ahistorical and, I believe, pedagogically unwise.

I have tried to produce a book that reflects how astrophysics is done rather than a stylized account of what is to be learned. There are occasional redundancies and recapitulations, but they are intentional, resulting, in part, from a deliberate effort to maintain the feel of lectures. For instance, some of the material that is included in Chapter 2 on instruments concerning calibration of absolute stellar properties is repeated in a different way in Chapter 5 on binary stars. By that point, you may have forgotten some of the ideas, and this way you will see it in a new context, with additional caveats on the application of the methods in pathological cases. Galactic dynamics, discussed in Chapter 7, draws heavily on material in Chapter 1, as does the derivation of the basic cosmological models in Chapter 8. Spectral types and Hubble galaxy classification are postponed until their respective chapters, but photometry is included in the chapter on instruments.

There is another feature of this book that I feel compelled to explain. You will frequently find extended qualitative discussion before getting to the analytical treatment. In fact, often I'll adumbrate a derivations in order to physically motivate the discussion. While some readers will find this an annoying habit, I hope you will bear with the presentation. Much of astrophysics is qualitative, and it is a tribute to the power of dimensional heuristic arguments that they serve as such effective guides when faced with diverse and complicated processes. This book isn't intended to be a formal axiomatic presentation of astrophysics. Progress often comes instead from the combination of observations and "horse sense," that elusive quality called physical intuition that the discussion aims at helping you develop. At the same time, the intuition is developed within a theoretical framework and this requires some lengthy justifications and derivations.

Contents: Chapter 1. From Gases to Clusters: Concepts in Gravitation and Gas. Chapter 2. The Raw Materials: Instruments and Observations. Chapter 3. Radiative Transfer and the Outer layers of Stars. Chapter 4. The Interiors of the Stars and Stellar Evolution. Chapter 5. Structure and Evoltuion of Close Binary Stars. Chapter 6. The Interstellar Medium. Chapter 7. Our Galaxy and Others as Stellar Systems. Chapter 8. The Biggest Picture: Cosmology.

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