Thus the basic geography of a black hole, familiar to every pilot in the Navy. If you fell through the event horizon you could never escape. You would be drawn inexorably into the singularity at the center, a place where the compression forces had exponentiated to the point where spacetime itself was ripped open. Pirius idly watched gaudy displays of exploding stars, Big Bang compression waves, and unlucky smeared-out cartoon pilots.

But now Draq said that the most productive way to think about a black hole was to imagine that the event horizon enclosed a separate universe. After all, nothing within the horizon could ever communicate with anything outside. It was as if a gouge had been ripped out of our spacetime, and another universe patched into the hole. In fact, he said, with an enthusiastic but unwelcome diversion into equations, that was how you dealt with a black hole mathematically.

Inside a conventional black hole, that new baby universe was doomed to implode forever into its singularity. But it didn’t have to be that way. What if that infant universe expanded? After all, that was how the outside universe seemed to behave, and it was possible for gravity to act as a repulsive force: the swelling of the universe itself was being driven by a field of “dark energy” with exactly that property. Draq said that—theoretically anyhow, under certain conditions—the great violence of the collapse of a massive object could shock a region of spacetime into a new configuration. And if that happened, yes, you certainly could create a new baby universe doomed not to collapse, but to expand.

But that expansion was limited. The mass of the collapsing object still drew in matter from the outside world, so there was still an event horizon, the distance of lightspeed escape. But now the horizon was like a stationary shock wave, the place where the infall from the parent universe outside met the expansion of the infant within.

This collision of universes created an “ultra-relativistic fluid,” as Draq called it, like the meniscus on a pond that separated water from air. This exotic stuff was gathered into a shell as thin as a quark, but a spoonful of it would weigh hundreds of tonnes. An unlucky infalling astronaut wouldn’t slide smoothly into the lethal interior, as she would if this were a conventional black hole. Instead, every particle of her mass would have to give up its gravitational energy at the shock front.

This “gravastar” was no black hole; it would blaze brightly with the energy of continual destruction. But even so, Draq said, outlining a paradox Pirius didn’t begin to understand, the temperature of the shell would only be a billionth of a degree above absolute zero.

Pirius failed to see the point of this. But he enjoyed the Virtual fireworks.

Nilis had become increasingly restless as this went on. At last the Commissary lumbered to his feet. “Yes, yes, Commissary Draq, this is all very well. But this is nothing but theory—and antique theory at that. No such ‘gravastar’ has ever been observed in nature.”