Galaxies: A Very Short Introduction

It's almost impossible not to be overawed by galaxies. As these pages tell us, the largest of them (giant ellipticals) contain more than a trillion stars spread over hundreds of kiloparsecs (1 kpc = 1000 x 3.25 light years). The most distant galaxies detected so far (using Hubble Ultra Deep Field) have shown up in a minute patch of sky that appears blank to other telescopes. Yet this patch, from an area about one thirteen billionth of the sky, contains over 10,000 galaxies, whose light started its journey towards us over 13 billion years ago. (How these proto-galaxies manage to emit light suggesting this immense distance/time when only 800 million years old is one of many questions you will probably ask yourself while reading. Most are answered in this book.) Future astronomers, looking beyond these primitive galaxies and using the next generation of telescopes, expect (and hope) to see ... nothing, for they'll then be looking at the 'dark age' between the Big Bang and the time when galaxies started forming. Such science is truly awe-inspiring. Modern cosmology began only in the 1920s, when Edwin Hubble made his two major discoveries (that independent galaxies exist outside our Milky Way and that there is a precise relationship between a galaxy's redshift and its distance). But cosmologists have managed to cover a lot of ground (and space) in the succeeding 80 years or so. It is to Gribbin's great credit that he manages to convey the essence of this progress in so succinct and accessible a manner - there aren't any equations in sight to vex the more mathematically challenged. For most general readers, the basic principles of cosmology are challenging enough already. But for those who know Gribbin's other books, they'll probably find the going easier here than in, say, Shrödinger's Cat. My only quibble concerns sequencing. After explaining how astronomers use the Doppler effect to calculate how stars are moving through space, Gribbin continues in a seemingly contradictory fashion: 'but the cosmological redshift is not caused by motion through space and is not a Doppler effect.' We have to wait 20 pages or so for the riddle to be resolved. Similarly, one of the graphs uses the Omega symbol several pages before explaining its significance. But such things aside, this is a superb introduction to a mind-changing subject. As in the better VSIs, non-specialists are helped by a straightforward Glossary which explains, for example, the difference between Galaxy and galaxy, and Universe and universe, usages which professionals take for granted but which confuse non-specialists. An outstanding introduction to the subject.

Essentially, this book presents a useful account of our Milky Way, the origin and fate of galaxies. Galaxies are made of hot bright stars and cool dark clouds of gas and dust. They can be defined according to their shapes. The Milky Way is spiral in shape with diameter not significantly smaller than the average and there is a massive black hole at the centre. It seems that the black hole and galaxy must have formed together. Without dark matter, galaxies could not grow at all. Most galaxies occur in clusters that are held together by gravity. Individual galaxies within the galaxies are moving around their centre of mass while the whole cluster is expanding in the Universe. The fate of galaxies depends upon the fate of the Universe which could be a Slow Rip, Big Rip or Big Crunch. In spite of this, the Andromeda galaxy is rushing towards us and will merge with the Milky Way in about 4 billion years' time!

‘Galaxies’ is a natural progression from ‘Stars’ in the VSI series but is much more reader-friendly in that it deals with the subject without recourse to equations and exotic maths. This said, the reader must be prepared for some very large numbers in terms of distances and if nothing else these demonstrate how inconsequential the Earth and the solar system are in the known Universe. Also how ridiculous it is to talk realistically about interstellar travel. The content covers both factual knowledge and those aspects of galaxies that are speculative or theoretical however all these are described in non-academic terms suitable for the general reader. The format is similar to ‘Stars’ in that it includes sections on the origins, formation, evolution, measurement of and the probable future scenarios for galaxies, plus an interesting account of how mankind has developed techniques and equipment to investigate these stellar bodies. Whilst there are a few concepts that may be difficult to grasp, the book is certainly written in the spirit of Very Short Introductions and worth reading.

A must-read for all those interested in the evolution of the universe and in finding out just how un-special we truly are in the grand scheme of things. A splendid light read that even a child could understand quite well, inasmuch as it can be understood. It doesn't go into specifics. It's mostly simple prose with basic explanations for some of the accepted hypotheses and theories of the day. Got it for an exam. Learnt a few cool things in it that I didn't find in my textbooks.

The author writes in a very lucid, fluent style. Very accessible. I am enjoying it immensely.

An interesting read, a bit smaller than I would have liked

A great quick read with understandable descriptions of different aspects covered in the book

Amazing vht

Quick and easy read. One of the best introductions to galaxies written by a master science writer for the lay audience. The discussion of galaxies shoehorned into a book about Cosmology. Not sure if this was the author's intent. The book was a bit sparse on how galaxies formed out of the dust and gases in the interstellar medium. A topic of particular interest to me.

Very good book. Easy language easy to understand.

A concise review of the subject. This volume is organized in the main around tracing the evolution in astronomy first toward the concept of ‘galaxy’ and then along the main thread of research done by the big names (Shapley, Curtis, Hubble) that refined our understanding of galaxies through various innovations in measurement techniques (parallax, Cepheids, novae, supernovae, etc.), arriving at the state of the art view of galaxies as of 2008 when this introduction was written. The author at times refers to VSI:Cosmology and these two works, while not technically companion volumes, might fruitfully be read together. For one well-versed in Astronomy and Astrophysics there is not much new here, though the review of the historical progress of thinking about galaxies is on the whole well done and gives the reader a solid frame of reference for the direction of astronomical research today and the strands of the main issues and the complexities and complications with which researchers have to contend. I, as an amateur astronomer, would have preferred a more systematic approach in some areas. For example, short shrift is given to types of galaxies; we learn there are spirals, ellipticals, and irregular galaxies, but there is nothing on the classification systems that have grown up over time (e.g. Hubble’s—S0, S1, ...). Nor is there much of any discussion of or attempt to organize the multifarious cavalcade of terms describing galaxies the casual astronomy fan will have heard over the years (e.g. Seyfert galaxy, de Sitter, etc.). I also found the [almost utter] lack of math somewhat irritating. Given that this is an introduction to the subject this perhaps should be rated an advantage for most readers. A survey must necessarily skate along the surface. Yet I found myself wondering, “Well how is that calculated?” or “What are the units of this quantity?” more than once. And with what math there is, it’s sometimes hard to tell where all the numbers are coming from. (Such as when we are told that a region of space 200 Mpc across yields a volume of 4 million cubic Mpc—but obviously 200*200*200 = 8 million. Did the author intend to refer to a rectangular volume with one side of 100 Mpc? With no additional details or diagram or reference, it’s impossible to say.) I would have liked a bit more on competing ideas and theories (such as alternatives to lambda-CDM). The book is really designed around working the reader up through history to arrive at the best current understanding. Anything considered speculative or cutting edge isn’t really covered. Sometimes the organization of the argument is poor and could have used some additional editing—for example the term cosmological redshift is used multiple times before it is explained in a later chapter. A little more care in explaining emission and absorption spectra and star Populations and star types (though I assume these may be treated more rigorously in VSI:Stars) would have been helpful. More tables or diagrams would have better delivered the crucial points along the way—such as a chart or graphic relating the assorted techniques to calculate distance and their strengths and weaknesses, or one showing the redshift curve (Z vs distance vs % light speed) or redshift horizons associated with different object types and observational techniques, or a graphic showing when and how early pre-galactic accumulations developed into proto-galaxies, then early galaxies, and so on. In fact there is not a single graphic showing the types of galaxies—what exactly is meant by a spiral galaxy? I also would have liked better references to the standard catalogues (such as RC3) that astronomers use. But on the whole this introduction gives the reader a good background of the controversies and open questions, and a coherent picture of what galaxies are, how they form, and how they vary. This book is not targeted at the specialist. But even so there are some good tidbits skimmed from modern advances sprinkled throughout, and some were news to me, such as the finding that the galactic core supermassive black holes are always 0.2% the mass of the matter in the surrounding spheroid (the galactic bulge). Overall good, not great: 4 stars.

Only negative is small print.

I really enjoyed this book, and it was a great companion to "Stars: A Very Short Introduction." Though I'm an engineer, I tend to favor popular science books that are lighter on math and that fascinate and offer more a intuitive treatment into a particular subject. There are plenty of other sources if one wants to dig further. "Galaxies" did not disappoint, and Gribbin's style is very friendly and engaging. Thank you, Dr. Gribbin. I highly recommend your book!