Gravity’s Engines by Caleb Scharf

The last week or so of silence on the blog has been due to my trip to Ohio (which was very enjoyable), and a lack of child care for the early part of this week. A day and a half home with both kids was just exhausting, but the trip was useful in that it provided me time to read Gravity’s Engines by Caleb Scharf, on the plane to and from Columbus (I got the paper edition at Science Online, and figured as long as I had a printed book I wanted to read, I might as well dodge the stupid argument about whether my Nook is likely to interfere with the plane’s navigation systems).

This book comes with the lengthy subtitle: “How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos,” which pretty well serves as a summary of the whole thing. You might be thinking “Why do we need yet another books about black holes?” but this is actually taking a different angle on the subject than most other treatments I’ve seen. Most popular books writing about black holes focus on the exceedingly weird effects of general relativity– the event horizon, the warping of spacetime, things like Hawking radiation and the information paradox. While those topics get mentioned here, the primary focus of the book is on the outside of the black hole, particularly the supermassive black holes at the centers of galaxies, and the titanic amount of energy released as matter falls into them.

This is a good topic for a book, because there’s really a mind-blowing amount of stuff being slung around. These black holes power quasars that outshine entire galaxies (in a fairly narrow beam, anyway) making them detectable across the entire visible universe. They also, counterintuitively, propel vast quantities of matter outward, producing gigantic “jets” extending outward from galaxy cores, and changing the flow of matter in galaxies and clusters of galaxies on a scale that boggles the imagination.

As we’re a Department of Physics and Astronomy, and three of my colleagues work on either galaxies or black holes, I’ve heard a lot about these subjects over the last dozen or so years, but never all laid out like this. Scharf brings together a wide range of material relating to galaxy evolution, star formation, and interactions between galaxies, and ties it all together in a compelling way. Having heard bits and pieces of research that ties into this story in a decade of colloquium talks makes it particularly nice to see everything brought together in one place. I wouldn’t say that this prior sorta-kinda-knowledge is in any way required to make this make sense, though– on the contrary, the basic ideas are explained clearly and comprehensively enough for a wide range of readers.

If I have any quibble about this book, it’s that it’s highly speculative, and thus incomplete. Scharf is making an argument for a very particular view of the role black holes play in the universe as a whole, but it’s not clear that this is in any way settled scientifically. A lot of the evidence he presents is more suggestive than conclusive, and there are a number of points where he basically punts on the details of some mechanism for how this stuff all comes together. Which is fine, as far as it goes– there’s no need to wait to talk about science until everything is nailed down and becomes boring– but it does leave the faint possibility that ten or fifteen years from now, new research will make the whole thing seem quaint and naive.

But then, whatever we may learn in the next ten or fifteen years of research isn’t going to help me pass the time on a couple of boring flights last week, which this book did. And it did an excellent job of that, so if you’re looking for something to read about truly cosmic events, I recommend picking this up.

Also, because I can, here’s a wholly gratuitous music video: