Adapted from Gravity’s Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos, by Caleb Scharf, by arrange­ment with Scientific American/Farrar, Straus and Giroux, LLC (US), Penguin Press (UK), Hayakawa Shobo (Japan) and Prószy´nski (Poland). Copyright © 2012 by Caleb Scharf.