Black Holes: a very short introduction - Katherine Blundell ***

Black holes have to be amongst the most fascinating phenomena of astronomy/cosmology and as such make a perfect topic for a new addition to OUP's vast collection of pocket guides, the 'very short introduction' books. I read my copy on a couple of 45 minute train journeys - it's long enough to give a good grounding in the basics of black holes, without being heavy or over-technical.

We are taken on a tour that includes the early black hole-like concepts, and the nature of the real thing, what would happen if you fell into one, the black hole's thermodynamics (which is more interesting than it sounds), how we discover things like their mass and spin rate, how they grow (and shrink) and plenty more. Considering this is just 93 pages, Katherine Blundell packs in the good stuff.

The writing style is generally approachable, and this is a popular topic, so I was all set to give the book four stars, but there were sufficient issues to pull it back down. The first was the errors. Almost every popular science book has at least one, but there seemed rather more than usual. The expected one, which I couldn't blame Blundell for, was in the description of Hawking radiation, which doesn't make a lot of sense. The reason I don't blame the author is that almost all popular science descriptions of Hawking radiation don't make sense, because all of us, except working physicists, assumed Hawking described it correctly in his book. Unfortunately he didn't - in attempting to simplify a messy theoretical concept, he came up with an 'explanation' that doesn't hold water, which was then, unsurprisingly, repeated elsewhere over an over. It's unfortunate timing that there has been a lot of publicity this year for this problem. 

Less forgivable were a couple of oddities. The Andromeda galaxy is described as being 6 million light years away. It is actually around 2.5 million light years. While you might argue this is order of magnitude correct, even the worst taxi driver wouldn't take you on a route that was 3.5 million light years too far. We are also told that white dwarf stars are cold. This seems to suggest a lack of understanding of stars - you can't radiate blue-white light and be cold. What might have been intended is that over time white dwarfs do cool in the way that ordinary stars don't, because there's no hydrogen fusion to heat them, but it's a very slow process and observable white dwarfs tend to be pretty toasty.

Finally, there's the matter of omissions. Most of the work on black holes is theory rather than observation, and there's a rich vein in the theory around, for instance, the concept of firewalls - whether an observer passing into a black hole would not notice the event horizon or would burn up, as some theories suggest. Other theories put the entire universe in a black hole, making the possibility of a holographic reality. It's a shame this fun speculation isn't there, both to see and be analysed, especially as so much about black holes is based on theory rather than observed data.

Not a bad book, by any means, but enough issues to raise a small flag.

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Review by Brian Clegg