Pleased with the image, he conjured up the other component of the queer hybrid vehicle.
Yggdrasil would make a compressed sort of dumbbell, he decided, with a short, thick handle and rather flattened hemispheres. More like a pair of fat wheels lying athwart the long axis of the probe. One hemisphere was silver with a green rim facing the fusion fire. The other was brown, laced through with the crystal sparkle of cometary ice and showing an arc of green where Yggdrasil’s root system had decided to help out with the photosynthesis.
The looming reality of a wall of foliage rushing past him only a few miles away dissipated the image, and Bram turned his eyes to the view he loved best.
Between the rushing walls of Yggdrasil’s twin hemispheres, a spectacular slice of sky was visible. A rainbow of stars made a dazzling arch across the void. Optical effects had crowded the bands of color so close together that the effect was like strands of matched jewels, jumbled together in overlapping profusion.
It was so beautiful that it hurt.
Bram studied the ribbon of stars. Was it narrower than the last time he had looked? It was hard to tell. But the yellow band seemed to have moved a degree forward, and the dull, ominous blanket of reds that faded into the blind spot seemed to have been dragged along by the rainbow hem.
A star whizzed by, changing from purple to blue to green, then to yellow, orange, and red before it was swallowed by the blind spot.
The star must have been very close—only a few light-days away. At the present gamma, Yggdrasil swept across a light-year in about thirty minutes. That was fast enough to make the nearer stars move at a crawl, changing their colors as they lined up against the background rainbow.
A second violet star popped out of nothingness, riffled through the spectrum, and vanished to the rear.
The first star’s companion! Yggdrasil was skirting a double star system.
Bram tried not to worry. Even here in the depths of the galaxy the stars were light-months apart. A collision would be most improbable, Jao had assured him. Even if Smeth’s instruments were to show Yggdrasil heading straight toward a star emerging from a dust cloud, there would be minutes—perhaps hours—to change course. A lateral nudge of less than half a degree, projected over a minute or two of travel, would always give them margin to spare.
He drank in the glittering, spectacle again, wondering how much longer he would be able to enjoy it. As Yggdrasil’s speed increased, eventually the stellar rainbow would shrink into a thin gold rim framing the forward blind spot, and the vortex of hydrogen influx would make it invisible from any part of the tree. He had tried to get a time estimate from Jao, but Jao had been vague. They were slicing the remainder of the speed of light so thin at this point, Jao said, that measurements were meaningless.
He looked up through the top of the pod and saw the trunk rushing toward him. A cluster of external housings was directly above: upside-down bubbles with suspended catwalks. Ten or twenty miles to his left, he saw a portion of the tremendous crystalline girdle that circled Yggdrasil’s waist and the secondary tether that would keep Yggdrasil from sliding forward along the shaft during deceleration mode. The tether was of woven viral monofilament a half mile thick, and the double bowline knot that fastened it had been tied, with much tricky maneuvering, by a pair of space tugs. Tension would only make it stronger; with the enormous forces involved, nobody wanted to take chances with extraneous fittings.
Bram noticed that at the moment Yggdrasil was floating free within its circlet; its momentum was temporarily matched with that of the probe.
The trunk filled his view, and then the taffy pull of the counterline slowed the travelpod to a bobbing stop about a half mile below the entry blister.
Bram uttered a mild expletive as he found that the fist-size electric trolley that was supposed to wind him in the rest of the way was out of order.
For a moment he was tempted to exercise a year-captain’s prerogatives and signal the hub to reel him in. But he was only a couple of hundred feet from his destination, and the pod’s weight was negligible added to his own, even under one-g acceleration. A half hour’s worth of muscle power would do it.
With a sigh, he bent to the two-handed windlass and began cranking.
“That ought to do it,” Bram agreed.
He tore his gaze away from the massive helical housing of the high-capacity pump. There was a final gurgle that shook the floor as the last of a half million gallons of chemical solution was forced deep into Yggdrasil’s sapwood.
The tree systems officer and her hovering assistant gave him bland stares. “I thought the best way to calm Yggdrasil down would be to smooth out the peaks and valleys in phytochrome balance,” the TSO said with professional briskness. “There was too extreme a swing between the two pigment forms, and it was driving Yggdrasil crazy.”
She gauged his expression for signs of comprehension, apparently decided in his favor, and went on. “You see, the problem is the growing Doppler shift. Unfortunately, all the far-red light comes from the same direction as the fusion light, so that side of the tree’s overstimulated. The phytochrome keeps changing back and forth between the far-red-absorbing form and the sunlight-absorbing form, then back again.”
Her assistant, even younger than she was, nodded agreement. They were both being patient with the old dodderer.
“Yes, yes,” Bram said quickly. “I’m sure you took the right approach.”
The assistant cleared his throat and glanced at his boss before speaking. “And at the same time, there’s the problem of blue light tropisms at the opposite side of the tree. Where the band of up-shifted light is. Yggie’s hormones are working overtime to cope. And you can imagine what that does to his biorhythms.”
“I can understand why your department was so concerned,” Bram told them in his best sober manner.
They both beamed at him.
“So we added a healthy dose of vitamin A to the tranquilizer to damp down beta-carotene activity,” the assistant finished triumphantly.
“Fine,” Bram said with a judicious nod. He looked around for a way to make his escape. “Well, that seems to take care of it, so I’ll—”
“Of course, you’ll want to review our total hormone strategy while you’re here, Captain,” Jao’s granddaughter said. “Shall we start with the tree-turning maneuver?”
Bram gave in to the inevitable and let her lead him over to the far end of the hollow, where a battery of young technicians, wearing the leaf tabards that seemed to be the working costume of the new generation, busily tended the array of giant fermentation tanks where hormone synthesis started.
A half hour later, his eyes slightly glazed, Bram found himself blessedly alone in the brilliant corridor that ran through the trunk’s heartwood. Alcoves branched off on either side, each with its neatly painted street sign. Here, forty miles beneath Yggdrasil’s bark, a lot of specialized work went on—plastics manufacturing using leaf sugars as feedstock, the Message broadcasting facility whose vital work could not be interrupted by yearly bough migrations, the central observatory.
There was also a recreation complex with guest suites, increasingly popular with the younger set and the advanced retroyouth crowd, with facilities for sports, swimming, and small-craft sailing. After Yggdrasil left the galaxy and acceleration ceased, it would be a center for such weightless pursuits as flying, flat-trajectory handball, three-dimensional ballet, and, Bram didn’t doubt, free-fall sex.
Bram paused to look at the bulletin board. Some members of the trunk staff were choosing up sides for a game of teamball in what would eventually be the flydome. Bram was tempted to join them. But he knew that he’d be invited only through courtesy and deference to his position. At his present chronological age, he’d only be a liability to whatever team was willing to suffer him; better stick to playing with his peers on the occasional Tenday.
Feeling pleasurably sorry for himself—refraining from reminding himself that he was not as old as he had been twenty years a
go—he gave the bulletin board a regretful last glance and set off down the long arcade toward the observatory.
At least that was one treat he could give himself.
Jun Davd looked up from his work and smiled at Bram with a third set of teeth that were as white and flawless as they had been when he had grown them a quarter century ago.
“Nice of you to play truant just so’s you can come visit an old man,” he said.
“The captain never plays truant,” Bram said, smiling back. “Everything I do is always in the line of duty.”
He raised both hands, and they touched palms in the old gesture.
Jun Davd chuckled. “So your duty brought you up to Yggdrasil’s attic to rummage through the stars.”
He was bent, frail, attenuated, but in remarkably good shape. Bram guessed that his biological age was down to about eighty. There were even traces of gray in the cap of white curls. Flesh was returning to the dark, mummified face, filling in the wrinkles. They had gotten to Jun Davd just in time.
“Is that what they look like now?” Bram asked, gesturing at the extrapolated display Jun Davd had been studying when he came in. The screen showed a splendid panorama of multicolored stars, glowing clouds, and luminous streamers swimming past in relative motion. Quite a few of the stars had disks.
“More or less,” Jun Davd said. “The computer’s having a hard time keeping up. That nice orange star you see coming toward you has been reconstructed from gamma rays in the ten-to-the-minus-six-nanometer range. The light that kills. The rear view’s even more of a challenge. We’re seeing those stars by ultralong radio waves—past the hundred-kilometer range. We’ve got almost a thousand miles of wire with a weight on the end trailing behind us for a dipole antenna, and I really could use a couple of thousand miles more except that I haven’t been able to figure a way to keep the drive from melting it, and I’ve got I don’t know how many thousands of stiff wires making pincushions out of Yggdrasil’s crown and root ball, but you can appreciate that definition’s still a problem. I’m afraid the computer’s taking a lot of artistic liberties.”
“Stop complaining. You’re living in an astronomer’s paradise.”
He grinned, young teeth white in the ancient face. “Don’t I know it. On my way to the galactic core to make direct observations of whatever the dust clouds are hiding. The old director, Pfaf-tlk-pfaf, would’ve given one of his fingertips for the chance!”
“I wonder what he’s doing now,” Bram started to say before he remembered.
It was strange to think that the old Nar, Pfaf-tlf-pfaf, had been dead for almost fifty thousand years. And that the immortal humans whom Yggdrasil had left behind were, presumably, still alive—unless the Father World had been hit by a wandering planetoid.
A wave of nostalgia washed over Bram as he remembered how kind the old director had been to a little boy who wanted to learn about the stars and how patient a human astronomy apprentice named Jun Davd had been in explaining all the wonders of the stellar universe.
“Sometimes I wish I’d followed my instincts back then and chosen astronomy as my career,” Bram said.
“I’m awfully glad you didn’t,” Jun Davd said tartly. “Where would I be now?”
It was a sobering thought. The two of them contemplated it in respectful silence for a moment, then Jun Davd went on more equably.
“It’s not too late, you know. You can have an infinity of careers if you wish. Why don’t we take up our lessons where we left off? In five hundred years you might make a pretty fair astronomer.”
“Are you offering me a job, Jun Davd?”
The dark face creased in mirth. “I’m going to need a good assistant. We’d better learn all we can about the Milky Way before we arrive there—including how to use its H-II regions and the hypermass at its core to match our impetus and bring us to a nice safe stop.” His voice was rich with enthusiasm. “Imagine being able to study a galaxy from the outside before making it your home! What an incomparable opportunity!”
Jun Davd had retired, still a junior apprentice, before the immortality project had borne fruit. He had hung on longer than most, and the Nar compassionately had looked the other way, but the day finally had come when he’d had to admit to himself how feeble he had become. He had been miserable in retirement. When Bram, with immortality finally in his pocket, had sought him out, he had jumped at the chance to join the expedition as chief astronomer, with the chance to run things to suit himself. In one swoop he had gone farther than he had in an entire lifetime on the Father World, and he had unlimited vistas before him. Bram sometimes thought that it was this, as much as the immortality treatment itself, that had rejuvenated Jun Davd.
It would be different now for humans on the Father World. Now it was the Nar who were the mayflies.
Their society had had fifty thousand years to adjust to the new truth. How had it transformed itself? Bram wondered. He would never know. And every hour another few years passed on the world he had left.
He shook off the thought and returned to the conversation.
“Are you sure we’ll find a hypermass to brake by when we get there?” he said.
Jun Davd looked at him reproachfully. “You’re forgeting all I taught you. Scratch a galaxy like ours and you’ll find a hypermass at the center. Relic of the quasar epoch. It’s a necessary consequence of the way galaxies are formed.”
“I know. A giant black hole.”
Jun Davd nodded. “A black hole with a mass of anywhere up to several hundred million swallowed suns. The centers of galaxies are violent places, and they’re very crowded. They stir up brews of colliding suns and relativistic electrons. They throw off x-ray jets. Sometimes they explode. The different events depend on the size and spin of the black hole and what it has to feed on and the way it chooses to express itself. And maybe the normal galaxies we see are simply the violent ones in a quiet phase of their history.”
“You paint a vivid picture. What kind of core are we diving into now?”
Jun Davd did not smile. “One that worries me,” he said.
Bram was instantly alert. “What do you mean?”
“For one thing, there are more young stars than theory predicts. And the infrared radiation getting through the dust clouds keeps increasing the farther in we travel, especially at the wavelengths associated with star formation. There are too many stars being born in there.”
Bram searched his rusty memory. “You told me yourself, years ago, that emissions at around the hundred-micron wavelength increase at a fairly uniform rate as you go in.”
“You don’t take my meaning. At this point we’re seeing by light that won’t reach the Father World for another fifty thousand years. We’ve jumped fifty thousand years into their future—and the future of those former selves of ours that made those infrared observations. The process, whatever it is, is speeding up. Something odd is happening behind those dust clouds. Something recent.”
“What do you think it is?”
Jun Davd switched off the display showing the outside stars and punched in a new code. A galaxy appeared within the screen, shining by the glossy light of computer simulation. It was a very pretty spiral with a regular shape. A second galaxy appeared to its left—another spiral, slightly smaller.
“You’re looking at our galaxy the way it appeared some hundreds of millions of years ago, before we collided with the Bonfire. The smaller spiral is the Bonfire as it must have looked before the encounter tore it all out of shape. You’re about to see a computer reenactment.”
“I’m impressed.”
“It wasn’t as big a job as you think. The basic computer model is an old one. I brought it aboard with my data files. I first ran into it as a young astronomy student. All I did was feed in a lot of updated data, including the fifty thousand years’ worth we’ve collected on our trip so far.”
“Go ahead. I’m ready.”
Jun Davd set the display going with a final poke of his finger. The point of view
rotated slightly to give more of a side view, and the smaller galaxy that was the Bonfire began moving toward the larger one. Their directions of rotation were opposite, like two wheels rolling toward each other.
“They’re going to grind together with a lot of extra kinetic energy,” Bram commented.
“Watch it here. We’ve got some tidal forces coming into play.”
The larger galaxy began to draw long streamers out of the Bonfire. At the same time its own spiral structure began to stretch and deform.
“I’m going to punch in a couple of overlays at this point,” Jun Davd said. “The red lines are infrared, the white ones radio.”
His long gnarled fingers played over the touch pad, and a pair of overlapping contour maps appeared, more or less conforming to the optical shapes, surrounding them with concentric squiggles and squeezing close together at the centers of the galaxies and in the areas of encounter.
The two galaxies continued to tear at each other as their arms brushed and mingled. It was not a head-on collision, but it was damaging enough. Gauzy ribbons that must have contained millions of stars were stripped away and left to evaporate into space. The computer could not infer the collisions of individual stars—such collisions would have been rare even if the two galaxies had fully interpenetrated—but it could visualize the effects of the gas clouds slamming together.
“Tremendous rise in temperature,” Jun Davd said. “And intense radio emissions.”
The superimposed contour maps writhed, grew brighter, pulsed faster and faster.
“Now, watch closely,” Jun Davd said.
The spiral arm closest to the encounter flared and turned blue as millions of new stars were born out of the clouds of disrupted gas. The Bonfire sailed past, now a blazing blob of light that had lost its spiral shape. The larger galaxy squeezed, then stretched, responding to the gravitational tug. The coils on the opposite side, now released, loosened and changed their pitch. The blue arm tried to follow the Bonfire, reaching after it and losing more stars in the process.
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