"How?"

Carter looked toward the voice in surprise. "What are you doing here, Senator?"

"I was still here at Firefly when the crisis occurred," Chou said. "It is my right to be kept informed. How are the neutrons being deflected, Doctor?"

"Firefly emits particles in a thermal spectrum," Carter explained. "That means there are some at every speed from zero to near lightspeed. The ones that are moving slowly tend to stay near the black hole, forming a sort of cloud around it, and it's this cloud that's deflecting the beams."

"Surely they can't change the beam directions very much," Chou argued.

"They don't have to," Rurik put in. "Firefly is much smaller than the neutrons themselves. But, Ray, we took that effect into account when we set our temperature limits."

"I know. All I can think of is that our subatomic particle theory must be wrong somehow. If there are some particles coming out of Firefly that we haven't taken into account, all of our temperature curve calculations will be off."

"Hell cubed," Rurik muttered under his breath. "I'll get the theory people on this right away. Maybe with the extra particle emission data Firefly's giving them they can figure out where we're going wrong."

"For the moment, that won't help us," Carter said. "What we have to do is get more mass into Firefly, and that as soon as possible. The hotter it gets, the denser that particle cloud becomes. Not much, since most of the particles emitted have high kinetic energies, but even a slight increase in the number of low-energy particles just makes things worse. What have we got that we can throw at the black hole?"

"We have a spare DeVega accelerator," Rossetti volunteered, "but I don't think that'll help any."

"Why not?" Senator Chou asked. "That would give you an extra neutron beam."

For an instant Carter had an overpowering urge to tell the Senator to shut up. None of them had the time to explain things to a layman. "DeVega dipole accelerators require very tricky and sensitive electromagnetic fields to function. On a ring the diameter of the accelerator platform we can place only three DeVegas, spaced one hundred twenty degrees apart. Any closer and their fields would interfere with each other."

"What about putting the extra accelerator farther out from the center?" Chou persisted.

"At the distance we'd need the beam would spread out too much to be useful. And before you ask, directly above and below Firefly are the charged plates that hold it in place, so we can't run a neutron beam through there. Paul, can we increase present flux any?"

"No way. We're already running them ten percent above spec maximum, though I don't know how long they can hold that. We may in fact have stopped the runaway—the temperature is changing so slowly now we can't tell if it's going up or down."

"Let's assume it's still going up," Carter said. "Anything else we can use?"

"We've got a few X-ray lasers," someone said. "They could be set up to fire at Firefly."

"I've already checked that," Rossetti said. "It won't give a significant mass increment, and might add an extra scattering component to the neutron beams."

"Sir?" Galton spoke up hesitantly. "I may have an idea."

"Spit it out, son," Rurik said brusquely. "This is no time to be shy."

Carter winced at the tone as Galton blushed slightly. The young man's reticence was clearly not shyness, but instead the result of guilt feelings over his part in this mess. Rurik had never been good at understanding human emotion, though. He had declared that the fault was not Galton's and, for him, that ended the subject. It would never occur to him that Galton might still be upset.

"Sir, the DeVegas will accelerate any neutral particle that has a reasonable dipole moment. If we used, say, iron atoms instead of neutrons, we might be able to reverse the runaway."

Rurik nodded slowly. "That might just work, Galton. You'll probably get fewer hits on Firefly because of heightened beam self-interference diffusion, but the ones that go in are fifty-six times more massive. And they'll be deflected less by that particle cloud around Firefly." He looked at Carter inquiringly.

"It's worth a try," Carter agreed. "Anyone know how long it would take to switch beam materials?"

"I checked, sir," Galton said. "The beam would only have to be off for ten minutes. And there's enough spare iron around for about ten hours of operation."

"If we can't reverse the runaway in that time we'll have to try something else, anyway." But to have the beams off for even ten minutes might prove disastrous. Carter weighed the options briefly, painfully aware of the need for speed. "All right. Galton, get the DeVega crews together and brief them. We'll switch just one accelerator for now—make it Beta. If it helps, we'll do the other two a little later. Paul, I suggest you get the control room people ready for the switchover. The rest of you go to your Emergency posts—I want to be ready if any problems crop up. Get to it."

There was a mad scramble for the door, but as Carter turned to leave he found his way barred by Senator Chou. "Dr. Carter, a word with you, please."

"I'll be up in a minute," Carter called to Rurik over Chou's shoulder. Rurik nodded and glided from the room, not bothering to use his Velcro shoes. "What is it, Senator?" Carter said when the others had gone. "Make it fast, please. I'm in a hurry."

"What are our chances of stopping it, do you think?"

"Is that what you wanted? I have no idea. You'll just have to wait until the rest of us know."

"I can't wait for certainties—probabilities must do for now. I have a duty to the people of Earth. If anything goes wrong here we will have to begin taking steps to protect them, and the sooner we start the fewer will have to die."

Carter looked at Chou with new insight. For the past several months he had seen the Senator as simply an opponent, a cardboard cutout violently and irrationally opposed to the Firefly Project. Now, suddenly, Carter saw him as a human being. "You really care about Earth, don't you?" he said softly.

"It's my profession to care, Doctor. You may recall that I wanted the black hole placed a good distance further from Earth, where it would have been less of a danger to both the planet and the Space Colonies. I am not anti-technology, despite your side's efforts to paint me so, but I wished for a larger safety factor."

"Senator, there wasn't a decent safety factor available. If we can't stop the runaway, Earth has had it no matter where Firefly is."

"I don't understand."

Carter took a deep breath. "If we can't stabilize Firefly's temperature, it will keep getting hotter and hotter. The hotter it gets, the faster it radiates its mass as energy until it basically explodes. According to current theory, in the last tenth second of its existence it will radiate with one percent of the sun's total power output."

Chou's eyes were very wide. "Good Lord! And you allowed this—this nova to be placed in Earth orbit? You must be insane!"

"Senator, if Firefly lets go anywhere in the solar system Earth is finished. The sun will go crazy with all that extra radiation hitting it. If the extra solar heat doesn't sterilize the inner system, the extra radiation will. But we had no real choice in the matter. I don't think more than a handful of people realize this, but if we had just ignored the black hole from the very beginning the same thing probably would have happened. Firefly was already too close to blowing. We didn't deliberately put Earth in danger, Senator; we were trying very hard to save it. And we still are. Excuse me, but I have to get to the control room."

—

It was an hour later before Carter was satisfied that the DeVega accelerator crews had the technique down well enough to be able to switch beam materials in the shortest possible time. The Project's chief design engineer, Felix Mahler, floated by Carter's shoulder as the control-room personnel waited for word that the changeover had been completed.