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so much hard radiation that the shell is fluorescing?”
    “Yes.”
    “And you also want me to believe that there’s an intelligent race inside that furnace sending us messages?”
    Vargas said, “There can be no doubt that the signals are coming from NGC 7293.”
    “Impossible!” Krug roared.“ Impossible! ” He slapped his fists against his hips. “A blue giant—only a couple of million years old to begin with. How do you evolve life at all, let alone an intelligent race? Then some kind of solar blowup—how does anything survive that? And the hard radiation? Tell me. Tell me. You want me to design a system that’s a good bet not to have life, I give you this god-damned planetary nebula! But how signals? From what?”
    “We have considered these factors,” Vargas said softly.
    Quivering, Krug asked, “Then the signals are natural phenomena after all? Impulses radiated by the atoms of your filthy nebula itself?”
    “We still believe the signals have an intelligent origin.”
    The paradox baffled Krug. He retreated, sweating, confused. He was only an amateur astronomer; he had read plenty, he had stuffed himself with technical tapes and knowledge-enhancing drugs, he knew red giants from white dwarfs, he could draw the Hertzsprung-Russell diagram, he could look at the sky and point out Alpha Crucis and Spica, but all of it was data of an external kind, decorating the outer walls of his soul. He was not at home in it as Vargas was; he lacked a sense of the inwardness of the facts; he could not easily move beyond the bounds of the given data. Thus his awe of Vargas. Thus his discomfort now.
    “Go on,” Krug muttered. “Tell me what. Tell me how.”
    Vargas said, “There are several possibilities. All speculative, all guesses, you understand? The first and most obvious is that the signal-senders of NGC 7293 arrived there after the blowup, when things were quiet again. Say, within the last 10,000 years. Colonists from a deeper part of the galaxy—explorers—refugees—exiles—whatever, recent exiles.”
    “And the hard radiation,” Krug said. “Even after things were quiet again, there’d still be radiation from that murderous blue sun.”
    “Obviously they would thrive on it. We need sunlight for our life-processes; why not imagine a race that drinks its energy a little higher up the spectrum?”
    Krug shook his head. “Okay, you make up races, I play advocatus diaboli . They eat hard radiation, you say. What about the genetic effects? What kind of stable civilization can they build with a mutation rate that high?”
    “A race adapted to high radiation levels would probably have a genetic structure that isn’t as vulnerable to bombardment as ours. It would absorb all kinds of hard particles without mutating.”
    “Maybe. Maybe not.” After a moment Krug said, “Okay, so they came from someplace else and settled your planetary nebula when it was safe. Why don’t we have signals from the someplace else too? Where’s the home system? Exiles, colonists—from where?”
    “Maybe the home system is so far away that the signals won’t reach us for thousands of years,” Vargas suggested. “Or perhaps the home system doesn’t send out signals. Or——”
    “You have too many answers,” Krug muttered. “I don’t like the idea.”
    “That brings us to the other possibility,” said Vargas. “That the signal-sending species is native to NGC 7293.”
    “How? The blowup—”
    “Maybe the blowup didn’t bother them. This race might thrive on hard radiation. Mutation may be a way of life for them. We’re talking about aliens, my friend. If they’re truly alien, we can’t comprehend any of the parameters. So look: speculate along with me. We have a planet of a blue star, a planet that’s far away from its sun but nevertheless is roasted by fantastically strong radiation. The sea is a broth of chemicals constantly boiling. A broth of mutations. A million years after the cooling of the surface,