Einstein was taken aback a few months later when Karl Schwarzschild, a German astronomer then serving on the Russian front, pointed out that the equations contained an apocalyptic prediction: Cramming too much matter and energy inside too small a space would cause space-time to sag without limit. No force known to science could stop it from becoming a sinkhole from which not even light could escape.

Einstein could not fault the math, but he figured that in real life, nature would find some way to avoid such a calamity. A century later, however, astronomers agree that space is indeed sprinkled with massive objects that emit no light at all. Call them cosmic roach motels. Stars, atoms, wisps of gas that trace their pedigree to the Big Bang — all of them check in, never to check out.

Many of them are supposed to be the remnants of massive stars that have burned out, collapsed and imploded in cataclysms like supernovas or the even more violent gamma-ray bursts visible across the universe.

Generations of theorists, including Stephen Hawking, using the telescope of the mind, have made careers investigating the properties of these objects only barely in the universe. But they are still arguing about just what happens inside a black hole and the ultimate fate of whatever falls in.

Nearly every galaxy seems to harbor one of these dark monsters, millions or even billions of times as massive as the sun, squatting at its center like Dante’s devil. The bigger the galaxy, for some reason, the more massive the void inside it. How that happens is a cosmic nature-versus-nurture question, and anyone’s guess.

“How does a black hole know how big a galaxy it’s in and when to stop growing?” mused David Hughes, the director of the Large Millimeter Telescope, “or, conversely, how does the galaxy know to stop feeding it?”

Left by themselves, black holes lie dormant with their mouths open. But when something — say, a wayward star or gas cloud — does fall toward a black hole, it is heated to billions of degrees as it swirls in a doughnut called an accretion disk around the cosmic drain. Black holes are sloppy eaters, and when they feed, jets of X-rays and radio energy can be squeezed like toothpaste out of a tube from the accretion disks. Astronomers believe this is what produces the energies of quasars, brilliant beacons in the cores of galaxies that far outshine the starry cities in which they dwell. “Paradoxically,” Dr. Doeleman said, “that makes black holes some of brightest things in the sky.”