Customer Reviews

Galaxies: A Very Short Introduction (Very Short Introductions)

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This book does a good job of integrating many advances in our knowledge of galaxies from the past 30 years or so. A great deal of what it discusses, especially about the origins and evolution of galaxies and the role of black holes, was pretty much unknown when I studied astronomy as an undergrad in the 70s. Since I hadn't kept on top of that field continuously since then, I learned a lot from the book.

That said, I'm not sure someone who didn't already know something about astronomy, especially stellar astronomy, will find it as satisfying. (A science book for a "popular" or general audience would probably be good enough background.) Although the author (JG) includes a glossary, he deploys a number of concepts that neither appear in it nor are explained in the main text, including "isophotal diameter" (e.g. @46), "gravitational radiation" (@103), "coupling" of radiation and matter and the notion that radiation has a "temperature" (e.g. @74). Also helpful for understanding some of JG's explanations would be an awareness of (i) nucleosynthesis (how the elements in the periodic table are synthesized in the centers of stars), which is relevant to JG's explanations of star formation and the differences between Population I and Population II stars, and (ii) the sort of sumo wrestling contest between gravity and radiation that keeps stars alive (relied on at e.g. 92).

A disappointment for me was that the book emphasizes galaxies for their relevance to cosmology -- which asks questions like where did the universe come from, and where is it headed -- rather than dwelling sufficiently on galactic astronomy. By analogy, this is like studying animals because of what they can tell you about DNA or evolution, rather than because they're interesting in themselves. (And like those life science topics, cosmology is currently a lot more trendy than astronomy.) For example, more pictures showing the shapes of different types of galaxies would have been helpful. JG mentions that what used to be called "spiral" galaxies (back when I was a student, and even more recently) are now classed as a sub-type of "disc" galaxy, since many pancake-shaped galaxies don't have spiral arms -- but the one photo of a "disc" galaxy has spiral arms clearly visible (@13). We're told that the Milky Way is a "barred spiral," but no picture of a barred spiral is offered. A picture of an elliptical galaxy and of a globular cluster would also have been helpful, since both are discussed and the distinction between them is important. This is really a missed opportunity, because one of the coolest things about galaxies is seeing pictures of them -- cameras are more patient than our eyes, and can see things that even if you were looking through a powerful telescope you could never see in real-time. Other important astronomical, rather than cosmological, topics that get too little attention are the interstellar medium and the nature of "dust." The latter is referred to several times, but its presence in photos is never pointed out; and what it's made of is never mentioned, so you never get to hear that there are clouds of it that contain organic molecules and other surprisingly exotic stuff. There are plenty of other volumes in the VSI series that have more pages (e.g. 140-150, compared to the 112 pages of text in this one), so a shortage of space couldn't be the problem. What's more, there already is a VSI devoted to cosmology. I hope that the missing background explanations, illustrations and astronomical topics will eventually be included in a fatter second edition.

For most of us, it's difficult not to be overawed by mind-boggling figures and concepts relating to the universe. The largest galaxies (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 managed 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.

As Gribbin tells us, 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 principles 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 move through space, Gribbin continues in a seemingly contradictory fashion: '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 matters aside, this is a superb introduction to a fascinating subject. As in the better VSIs, non-specialists are helped by a very straightforward Glossary which explains, for example, the difference between Galaxy and galaxy and between Universe and universe - usages which professionals take for granted but which could easily confuse the general reader.

The Galaxies which deals with a subject that is usually beyond my ability to grasp is written clearly for the non-physicist. In addition for the casual reader who is not about to sit for his doctorate the length was appropriate. I highly recommend the book to those who wish to be informed about what is going on in the world of astrophysics but who like myself are casual readers of the same.

Of all the astronomical objects that are visible to the human eye, perhaps the most fascinating ones are the galaxies. This is in large measure due to the most familiar spiral galaxies, of which our own Milky Way is an example. Their twirling, irregular shapes are fascinating to the eye, for more or less the same reasons that the rings of Saturn attract attention. They are an exception to the universe that is filled with perfectly spherical or pointlike objects, with very little of internal structure. And just like Saturn, the fascinating shape of the galaxies has only been revealed with the advent of a telescope, and not until well into the 20th century did we realize that these "island universes" lay far outside out of the Milky Way.

If you are interested in finding out more about galaxies, what they are, how did we come to know about them, how they develop, and what their ultimate destiny is, then John Gribbin's book is an excellent introduction to the subject. It is accessible to a non-expert, and very little scientific understanding is assumed. It is very readable and interesting, and it will take a reader on a fascinating intellectual journey across the universe. After reading this book, you will be looking at the universe with a whole new set of eyes, and would hopefully appreciate our own place in cosmos.