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Astrophysics
WORLD SCIENTIFIC SERIES IN ASTRONOMY AND ASTROPHYSICS
Editor: Jayant V. Narlikar
Inter-University Centre for Astronomy and Astrophysics, Pune, India
Published:
Volume 1: Lectures on Cosmology and Action at a Distance Electrodynamics
F. Hoyle and J. V. Narlikar
Volume 2: Physics of Comets (2nd Ed.)
K. S. Krishna Swamy
Volume 3: Catastrophes and Comets*
V. Clube and B. Napier
Volume 4: From Black Clouds to Black Holes (2nd Ed.)
J. V. Narlikar
Volume 5: Solar and Interplanetary Disturbances
S. K. Alurkar
Volume 6: Fundamentals of Solar Astronomy
A. Bhatnagar and W. Livingston
Volume 7: Dust in the Universe: Similarities and Differences
K. S. Krishna Swamy
'Publication cancelled.
World Scientific Series in Astronomy and Astrophysics - Vol. 8
An
I n v i t a t i on to
Astrophysics
Thanu Padmanabhan
Inter-University Centre for Astronomy and Astrophysics, India
\jjjp World Scientific
NEW JERSEY • LONDON • SINGAPORE • BEIJING • SHANGHAI • HONG KONG • TAIPEI • CHENNAI
Published by
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British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
The background picture used in the cover design was adapted from the figure kindly provided by
J. S. Bagla. The N-Body simulations, from which the picture was developed, were performed at the
Cluster Computing Facility in the Harish-Chandra Research Institute.
AN INVITATION TO ASTROPHYSICS
Copyright © 2006 by World Scientific Publishing Co. Pte. Ltd.
All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means,
electronic or mechanical, including photocopying, recording or any information storage and retrieval
system now known or to be invented, without written permission from the Publisher.
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ISBN 981-256-638-4
ISBN 981-256-687-2 (pbk)
Printed in Singapore by World Scientific Printers (S) Pte Ltd
In memory of the late Shri Neelakanda Sarma, who introduced me
to the fun of doing Science.
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Preface
This book is exactly what its title claims to be. It is an invitation to
students and researchers in different areas of physics to share the fun and
excitement of astrophysics.
During the last two decades, technological advances have allowed us
to observe the cosmos with unprecedented accuracy, making astrophysics
and cosmology branches of science driven forward by observations. This
excitement and growth has attracted more people to enter this area and,
given the current enthusiasm, it is inevitable that astrophysics will continue
to be a leading branch of science in the early part of this millennium.
This subject has also fascinated the layman all through the ages, re
sulting in a proliferation of popular articles and books. Every branch of
astrophysics, of course, has excellent text books authored by the experts.
There are also a few comprehensive text books at an advanced level in
tended for serious researchers in the field. In spite of all these, currently
available literature leaves a gap which the present book is designed to fill.
This book will be useful, for example, to a theoretical physicist who wants
to have a quick overview of the entire subject of astrophysics — and appre
ciate the excitement — but without getting lost in the details. In a way, it
is expected to serve as 'a guide to astrophysics for an intelligent outsider';
maybe a researcher in theoretical physics, a student of physics or even an
observational astronomer who wants to dabble a bit with the theory.
I have designed the book keeping the above perspective in mind. To
begin with, it is by no means expected to be comprehensive. For that,
there are other books (including the three volume course of astrophysics,
running to about 1800 pages, authored by me and published by Cambridge
University Press). The choice of topics here stresses both the foundations
and the frontiers, moving lightly over anything in between.
Vll
V1I1 An Invitation to Astrophysics
Second, I have made sure that the book is self contained as far as astron
omy and astrophysics are concerned. For example, astrophysics, like every
other subject, has a collection of jargon specific to it and I do not expect
the reader to have any familiarity with this jargon. Astronomical jargon is
explained in the language of the physicist so that the book is accessible to
a wider community. The same criterion is used in the choice of theoretical
foundation that is laid in the first three chapters. These three chapters deal
with those areas of theoretical physics which are widely used in astrophysics
but might require some amount of brushing up for an average student of
theoretical physics. For example, bremsstrahlung or ionization equilibrium
or the propagation of a shock wave may not be a part of every researcher's
arsenal even though they might have learnt basic electrodynamics or fluid
mechanics. The first three chapters gather together several such topics in
order to make this book self contained. At the same time, I have not tried
to teach the basic areas of theoretical physics; I expect the reader to know
the basics of classical and quantum mechanics, special relativity, electro
dynamics, etc. (But not general relativity, which is introduced briefly in
Chapter 1.)
Third, I have added a fair number of exercises at the end of each chapter
which will provide some amount of practice for the physicist in applying
the concepts to astrophysical contexts. In particular, there are quite a few
problems titled 'Real Life Astronomy' which take the reader directly to
published literature.
Fourth, I have kept the algebra to the minimum commensurate with
clarity. Whenever the derivation of an equation is straightforward (even
though lengthy), I have merely indicated how the result can be obtained
rather than hold the reader by hand and take him/her through the algebra.
I think this allows for a crisper pace and those who are interested in the
key concepts and results can always take algebra for granted.
Finally, I have tried to keep the discussion in the later chapters fairly
topical. The emphasis is on research areas which are currently popular
rather than on more traditional topics. This has the disadvantage that
some of the ideas might change a bit over the next decade or so but the
advantage of conveying the current excitement in the frontier areas more
than compensates for this.
The cognoscenti will find that many of the derivations of even stan
dard results (Kepler problem, Compton scattering, Kompaneets equation,
Schwarzschild metric, gravitational lensing deflection ...) are different from
the ones usually found in textbooks. Hopefully, even the experts find some-
Preface IX
thing new and enjoyable in this book. I have also not shied away from
discussing some of the topics usually considered to be rather advanced but
the physical content of which is quite simple (for example, the concept of
black hole temperature).
The idea for this book originated from several colleagues who suggested
to me that an introductory text, to supplement my three volume course
in astrophysics, will be a useful addition to the literature. I was initially
hesitant since such a book will necessarily overlap to a certain extent with
the existing textbooks in the market, including mine. However, many peo
ple convinced me that there is really a need for such a book and some
amount of overlap will do no harm. I am thankful to J.V. Narlikar, who is
the editor of this series published by World Scientific, for an enthusiastic
and positive response. I thank L. Sriramkumar for reading the manuscript
and giving extensive comments. I have also benefited from my discussions
with K. Subramanian, R. Nityananda, D. Lynden-Bell and the members
of the Astronomy Division of Caltech regarding several aspects of peda
gogy related to astrophysics. In particular, K. Subramanian tried out parts
of the material in the book in an introductory astrophysics course he was
teaching at Pune University. I am also grateful to R. Gupta, H.M. An-
tia, C.C. Steidel and Jim Kneller for providing the data which were used
in generating some of the figures. As I have already mentioned, it is im
possible to avoid certain amount of overlap in the discussion with other
existing text books including my own Theoretical Astrophysics Vol I-III
published by Cambridge University Press. I have referred to this and other
text books wherever appropriate in the Notes and References at the end of
each chapter.
It was a pleasure working with Ms Magdalene Ng and her World Scien
tific team in this project and I thank them for excellent processing of the
book.
I thank Vasanthi Padmanabhan for dedicated support and for taking
care of the entire latexing, production of figures and for formatting the
text. It is a pleasure to acknowledge IUCAA for the research facilities and
ambience it has provided.
T. Padmanabhan
