Gravity’s Engines

Before reviewing Caleb Scharf’s Gravity’s Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos, a beguiling attempt to create a layman’s map of the known universe, I want to be clear: I am a layman, or rather, a laywoman. As a poet and professor of writing, I’m about as far from an astrophysicist as it’s possible to be. So when this book about the role of black holes in shaping the fates of stars arrived at our house ready to review, I demurred. Instead, my husband found it. He took it on his commute to work. He brought it to bed. He brought it to the dinner table. He began ignoring me, as if devoured. He was sucked away as if into a long dark void. Then, drawn in by the pull of his attention, I had to see what this fuss was about.

For several weeks, I too was lost, babbling about neutrinos and event horizons to anyone who would listen. Yet this book, which brought back all the wonder of a first visit to a planetarium, is no dark star. It is spangled with all matter of dazzlingly interesting stuff.  In it, Scharf, prizewinning science blogger and director of Columbia University’s Astrobiology center, explores things like the “primordial remains of the hot young universe”; the millions of ancient neutrinos cast off from the sun’s birth that now pass through each of our skins each second; and current galactic models that resemble “the dendrites and neurons of some megalomaniac artist’s weblike cosmic brain.” 

This is not just physics for poets. Scharf has also rendered one current critical puzzle for physicists — a mesmerizing study of how black holes actually are not themselves mere voids, but generative forces, thresholds of potential energy that act in much the same way dams on earth do. On earth, in a dam, there is pressure on one side and a lack of pressure on the other. Water forced through spillways, driven by gravity, generates enormous energy that we harvest as electricity. In a black hole, there is the universe on one side and a void on the other. And as stars and particles rush towards black holes, they pick up speed, sloshing in much the same way water does heading towards a dam or drain. Just as sloshing water represents lost energy we hear converted to gurgling sound waves, stars and gasses rushing towards the brink of a cosmic drain lose particles that can be “seen” translated into other forms of energy. The edges of black holes are thus always spewing matter, a kind of cosmic splatter paint. Although things pulled towards black holes are mostly swallowed, over time the sloshing of nearly swallowed stars spews the universe with a mess of Jackson Pollock-like cosmic goo. 

This dissolving star glop, Scharf wants to let us know, is actually the universe’s generative mess. The things that splatter on the edges of black holes can themselves become new stars, or, can float as gasses that rearrange the galaxies they are in, or even the planets near them. The very fact of life on earth is certainly a gift of the random seepage of the right elements at the right time — a happy mix of carbon and nitrogen and oxygen, a little iron, a smidgen of gold. Our planet as we know it is the gift of imploded stars. But “black hole dams” can take as well as give. Even our atmosphere rests at the whim of the black hole nearest us, the one at the center of our galaxy. One belch of the wrong stuff and we might lose our lovely ozone.

To call this an absorbing read is an understatement. I felt dreamily transplanted. If Scharf forgets to define a few technical terms, if occasionally his subjects are dense as a dwarf star, his writing also has a lightness of touch. At its best the book lets us into what is vast and hard to name, helping us feel our smallness and youth and contingency as beings. When I did emerge from the book to look up at the summer stars, the night seemed more brightly lit, slightly more known but also more awesome, more wonderfully strange.