In a 1783 paper English scholar John Michell envisioned a voracious cosmic monster: a star that was massive enough that its gravity would swallow light. He speculated that many such behemoths might exist, detectable only by their gravitational effects. Two centuries later, in 1967, American physicist John Wheeler gave the idea an evocative name: black hole. Just a few years afterward, in 1974, British astrophysicist Stephen Hawking taught us that black holes aren't so black after all: they emit radiation and will eventually evaporate.
Yet we've learned a lot since then about these destructive cosmic engines, as you'll find in “The Benevolence of Black Holes,” this issue's cover story by Caleb Scharf of Columbia University—and an excerpt from the latest entry in our Scientific American book imprint series with Farrar, Straus and Giroux. Starting on page 34, the feature article explains how the feeding habits of black holes can have surprising effects on the galaxy they occupy.