Seeing Jao redden toward explosion, Bram said. “Take pity on the man, Jun Davd.”
“Here it is translated into audio,” Jun Davd said. “With a little guesswork, of course.”
He flipped a switch, and the room was suddenly filled with clicks and snaps, as if a million demented children were all breaking twigs at once.
Bram felt ice down his spine. “What is it?” he said.
“It has no information-bearing content that we can see. On the other hand we can’t make it correspond to any natural radio phenomenon that we can imagine.”
Trist broke in. “So we decided it must be a by-product of some artificial process. Like back-lobe leakage from the space-based antennas of solar power satellites.”
“Then an analysis of the wave forms suggested strongly that the clicks were acoustic in nature,” Jun Davd said. “So we discarded the idea that they were some kind of static, either natural or artificial.”
Bram listened to the hard, dry snapping sounds for a moment. Regarded as actual physical noises, they were even more puzzling. “They’d have to be produced in a medium: solid, liquid, or gas,” he said.
“Ridiculous,” Smeth said. “There must be a natural explanation. Remember how pulsars fooled the early radio astronomers? It’s some property of the stars in this arm of the galaxy.”
Bram frowned. “Trist said that the signals come from everywhere. From the invisible star we’re orbiting too?”
“No. Everywhere but,” Trist volunteered.
“Now we come to the interesting part,” Jun Davd said. “Bear with me a moment. This is still very crude. But it will give you an idea.”
He fiddled with a console, and a holographic window lit up in the display board. It was a three-dimensional star map, reasonably realistic, with points of colored light scattered through the velvet darkness. A dull red bead began winking in a lower corner.
“That’s our position,” Jun Davd said. “Or the position of our infrared star. We’re somewhere in the cometary belt—we won’t quibble about half a light-year or so. And now here’s the route we took from the center of the galaxy.”
A yellow dotted line grew from the blinking bead, angling inward in the holographic illusion, and disappeared behind the windowframe on the opposite side.
“Now, all of this space is filled with these odd radio emissions—they’ve all had different times of origin and the oldest of them are presumably spreading in spheres many hundreds of light-years in diameter. Far beyond the boundaries of my little map. But that’s not what we’re concerned with. We want to show the stars of origin.”
He fiddled with the console again, and a whole swarm of stars in the center of the holo image began blinking. The swarm was in the shape of a lumpy sphere—as near to a perfect sphere as the actual distribution of stars in space could make it.
With one exception. There was a curiously flat, squashed area on the part of the sphere directly opposite the bead representing the infrared star, which hung just outside the boundary of winking stars.
“I don’t think that part of the sphere is actually flattened,” Jun Davd said. “That’s about forty light-years away—at the furthest distance from us. I think any emissions originating there have started fairly recently and simply haven’t reached us yet.”
Trist nodded in agreement. “Yes, we intersected a small chord of this … spherical volume of space on our way here, and when we crank back the data we find that we’ve witnessed several discrete jumps in the size of the globe. It seems to be growing quite uniformly, at about one-tenth of the speed of light.”
Jun Davd’s fingers flicked buttons, and a star at the surface of the shell sent a spray of three dotted lines toward the line embedded within the sphere that represented Yggdrasil’s route, making an equilateral triangle bisected at the vertex. He added three little green Yggdrasils where the dotted lines met the route.
“No reception,” Jun Davd said, tapping the first Yggdrasil at the earliest position on the route. He went on to tap the second Yggdrasil, where the bisecting line showed the shortest distance to the star. “First reception,” he said. Then he pointed to the third little tree symbol. “And we’re still receiving at the same radial distance as the previous no-reception zone, so knowing our speed and the distance covered, and throwing in a little Doppler anaylsis of about a dozen similar cases, we get a pretty good value for the rate of growth of the shell.”
“And virtually every single star within the shell is giving off radio clicks,” Trist said.
The other three looked at one another. The thought was inescapable. “Original Man?” Bram said.
“No, impossible!” Jao said.
Smeth was getting excited. Too excited. “Why are we wasting time here?” he said. “Whatever this phenomenon is, it’s growing from a center.” He squinted at the pinch of stars in the middle of the representation—a couple of yellow dwarfs, one with a smaller orange star and a red dwarf for companions; a solitary red dwarf; a blue-white giant attended by a burnt-out cinder. “Let’s investigate the center of the sphere and see if we can find out what’s causing it!”
Jao bellowed in outrage. He could see his lovely enclosed star slipping away from him. “What? That’s twenty light-years away! You’re talking seven, eight years of ship time by the time we build up enough gamma at one g! We’re here now! We can be at the center of this system in less than two years!”
Jun Davd was no help. He stood there smiling. Bram turned to Trist. “How fast did you say that sphere of clicking stars is growing? At about one-tenth the speed of light?”
“That’s right,” Trist said.
Bram exercised his prerogatives as year-captain. “In that case we can stay here and wait for it. This star is due to give off clicks any time now.”
CHAPTER 6
The sky was full of disks.
The nearest one, only a hundred million miles away, turned half the sky blind. It stood almost edge-on—seen only as a paper-thin rim faintly traced by light, sketching the partial outline of a tall ellipse whose shape could be inferred from the stars it blotted out.
It was immense. Unbelievably so. A planet would have been imperceptible against it, a sun a mere pinprick. Its diameter was, in fact, that of a planetary orbit.
Another disk, equally huge, bracketed the other side of the sky, showing as a somewhat fuller ellipse. But this one presented its inner face and was visible as a pale wash of refracted light.
Between them hung a whole collection of similar shapes, like paper cutouts all dangling at the same level from invisible threads. Directly ahead was a great illuminated circle on what must have been the opposite side of the hidden sun. A smaller circle was a black silhouette trying unsuccessfully to eclipse it. On either side of the smaller circle were attendant disks, canted inward to make narrow ovals. Their inner faces, closer to the unseen sun than the gigantic disk opposite, made brighter daubs against its inferior illumination. A bite had been taken out of the edge of one of them by the eclipsing circle.
Through the spaces between them could be seen a whole swarm of still smaller disks—if objects that were millions of miles in diameter could be called small. The glimpsed shapes were in a different plane than the outer disks; the ellipses they presented were horizontal, not vertical.
The tiny dot of a sun in the center of that bewildering arrangement had never peeped forth again in all the two years they had been traveling toward it. In view of the complicated schedule of eclipses, its brief emergence must have been an exceedingly rare event.
Bram stared over the heads of the crowd at the flat, queer shapes floating in the darkness. He swallowed hard. Reason said they could not exist. But they did.
“There can be no stranger sight in the universe,” Jun Davd said to no one in particular.
People jostled and crowded around him at the safety rail in front of the long, curving observation wall. This was a real view, not a holo. Naked space was on the other side of the transparent polycarb
onate sheet, and people had been gravitating here even though Yggdrasil’s slow rotation periodically turned the scenery on its head. The holo still ran at the opposite end of the lounge, but even though it showed close-ups, there was no added detail to make it worth watching.
“It works out to an ingeniously timed energy trap,” Jao was burbling to anyone who would listen. His burly form was at the center of a knot of people, the nearer ones in danger of getting clipped by his waving hands.
“Listen to him,” Smeth grumbled to Bram. “You’d think he was taking credit for it himself. It’s nothing like the continuous bubble he theorized about.”
“…though the timing’s decayed somewhat after seventy-four million years,” Jao went on. “Otherwise, we wouldn’t be seeing the disks by so much leaked light, and we never would have seen the star itself.”
A pretty admirer who must have stretched Jao’s uxoriousness to the limit spoke up. “I know you explained it before, Jao, but it’s awfully confusing. It gives me a headache just to think about it.”
“It’s beautiful, beautiful!” Jao boomed. “Look, there are four shells of disks—an outer and inner shell in equatorial orbit, and an outer and inner shell in polar orbit. The polar shells are the itsy ones on the inside, and their main job is simply to reflect all radiation into the equatorial plane.”
“I understand that, but…”
“Each shell consists of three disks whose diameters are equal to the radii of their distance from the sun. Actually, it’s their centers of gravity that’re in that orbit. But they don’t swivel. Each one of them has exactly enough spin to make its day equal to its year, so that the flat side always faces sunward.” He frowned. “Except that one of the inner ones once got a nudge from something that messed up its synchronization—probably a solar flare. That’s why the sun was able to pop out in the equatorial plane when we were in the cometary belt.”
“But why don’t they all just crash into one another?” his admirer wailed.
“Look—each set of three consists of disks whose centers of gravity are at the points of an equilateral triangle, thus occupying the same orbit in a state of equilibrium. It’s a very stable arrangement. And the fact—now, get this—the fact that the diameter of each disk is equal to the radius of its orbit means that the zone of interception of the inner set is equal to the zone of interception of the outer set—so that when you project that cone, it’s like having a solid fence of six disks, all tangent to each other.” He smiled benignly. “Except that you don’t have to worry about them crashing together. To say nothing of all the mass you save.”
“By using littler disks?”
He nodded. “Almost all the mass of the energy trap is in the three big ninety-million-mile disks. The next shell inward—the one that orbits at thirty-six million miles—contains only about a sixth as much mass. Call it four twenty-fifths. And the ratio holds as you keep diminishing—so that all of the inner disks put together add up to less than the mass of one more big disk. Original Man was very clever. He made his fence out of geometry instead of mass.”
“It’s a fence with a lot of gaps, though, isn’t it?” said a smart aleck who looked as if he were the boyfriend of the girl or aspired to be.
“Not as much as you think,” Jao said indulgently. “Let’s figure it out. Hey, Smeth, what’s the formula for a hypocycloid—never mind, I’ll graph it.”
He grabbed for the touch pad he had dangling from a chain around his neck and poked at it with thick fingers. An electric-blue circle grew on its photoplastic surface, followed by a horizontal line that bisected it, then two curves with the same radius as the original circle that sprouted from the ends of the line and met at the top. Little boxes began to subdivide the resulting figures, getting smaller and smaller until the eye could no longer separate them. The negatively curved triangle in the center differentiated itself with a change of color. Jao’s fingers asked the touch pad a couple of questions, and he read off the answer.
“Yah,” he said. “The equatorial fence intercepts about seventy percent of the solar energy that comes its way. So does the polar shell. Together they cover somewhat more than one-fifth of the surface of an imaginary sphere enclosing the sun at any radius. I guess that was good enough to do the job.”
“What ever happened to Jao’s Bubble?” his opponent asked maliciously.
Jao was totally bland. “Oh, yah, the idea of enclosing a star inside some kind of a continuous shell. It wouldn’t work.”
“I can’t stand it!” Smeth groaned. “Now he’s going to disown the whole idea.”
“He has no shame.” Bram laughed. “Jao throws off ideas, but. he isn’t attached to them.”
Jao was lecturing the young man earnestly. “In the first place, there’s no way to keep it from drifting off center,” he said. “You might start with the star perfectly centered, but once the slightest drift started, it would keep getting worse, because the attraction from all other directions would keep decreasing…”
“That’s exactly what I told him,” Smeth complained to Bram.
“…and can you imagine the centrifugal force at the equator if the thing rotated at all? Your sphere would suffer from slump. Everything would tend to collect at the equatorial plane. No, my friend, your sphere’s a picturesque idea, but you can’t have it.”
“How does he do it?” Smeth grumbled.
“And who needs it, anyway?” Jao said before his young antagonist could open his mouth to protest. “Let’s figure out how much energy Original Man had at his disposal for his intergalactic beacon.”
He reached for his pendant touch pad again and began tapping at it one-handed without looking.
“Look at him showing off,” Smeth said in disgust. “He hits wrong numbers all the time that way, but that doesn’t stop him.”
“Each one of those big disks has a surface area of … hmm … call it six point three six quadrillion square miles. A six followed by fifteen digits. On each side. If you’re trying to make sense of a number like that, it means that—” He punched numbers again. “—one side of a disk has thirty-two million times the surface area of an ordinary planetary body like the Father World.”
“Why one side?” his admirer queried.
“We’re only concerned with the side that’s soaking up energy.”
“Oh.”
Jao continued. “We’ve already got a value for the solar constant at the distance of the cometary halo, a light-year out. Now let’s crank it back according to the inverse-square law, and we’ve got—” His fingers busied themselves again. “At ninety million miles, it works out to … hmm … one point four kilowatts per square meter … times sixteen times ten to the nineteen square meters—”
“Oh, for pity’s sake!” Smeth burst out. “All that rigamarole! He wants to say that each of the three large diskworlds receives twenty-three times ten to the twenty-first kilowatts of energy!”
“Thank you, Smeth,” Jao said equably. “Twenty-three sextillion kilowatts. And we’re not through yet. We multiply by six, and—”
“Multiply by three something, you mean,” interrupted his rival for the young woman’s attention.
“No. Don’t forget the three disks of the inner equatorial shell may be a lot smaller, but they’re closer to the star, and they intercept exactly as much solar radiation as if they were big disks in the outer orbit.”
“But—”
Jao sailed on serenely. “Which means that in the equatorial fence alone, Original Man had one hundred and thirty-eight sextillion kilowatts at his disposal to turn into radio waves.” He paused for effect. “That is ten trillion times as much power as Nar civilization produced on the Father World.”
Bram caught his breath. The figure was staggering. He had never bothered to work it out himself, though he had known it must be very high.
“They thought big, those people,” he said to Smeth. “By now the human genetic code will have reached the Virgo cluster. I always assumed that was the targe
t. But with that kind of power, I wonder if they were aiming beyond.”
Smeth snorted. “Huh, don’t let Jao’s raving impress you too much. We don’t know how efficient those … constructions were at converting energy into the longer radio wavelengths and modulating them.”
“It hardly matters, does it?” Bram responded. “The waves will keep spreading through the universe. If they were meant to reach Virgo, the limit of their detectability must lie many times beyond it.”
Over by the view wall, Jao was unleashing one of his terrifying smiles on the girl. Though he was utterly faithful to Ang, he didn’t mind going through the motions.
Jao’s young competitor glowered and made another try at impressing the girl. “If most of the mass of the system is in the big disks,” he said belligerently, “how come the sun hasn’t drifted toward one or another of them over a period of time—just as it would toward one side of a ‘Jao’s Bubble’? Excuse me—‘Jao’s shell.’ The same thing would apply—the attraction of the other two disks would decrease with distance, and it would keep getting worse!”
He must have been a physics, apprentice. He stole a glance at the girl and went on in a classroom voice. “In a synthetic system like this one, which is essentially three big masses mutually revolving at the points of an equilaterial triangle, a mass occupying the center can’t move above or below the equatorial plane because of the combined pull of the three major components.” He stared a challenge. “But it can and will move within the plane!”
“I didn’t say most of the mass of the system was in the big disks,” Jao said kindly. “I said the big disks contain most of the planetary mass. Actually, they only mass about the same as a good-size gas giant—maybe a few tenths of one percent of the mass of the G-type star in the middle. So they’re in orbit around it in the normal way.”
“But that would mean—”
“Right. We know they’re very thin—maybe as little as fifty miles across the rim. But even so, with a diameter measured in orbital distances, that would give them a volume of maybe four thousand times the volume of your run-of-the-mill gas giant. So they’re lighter than they have any right to be.”
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