Diaspora by Greg Egan
Lac G-1’s fate seemed unavoidable, and the signal reaching TERAGO certainly confirmed the orbit’s gradual decay. One small puzzle remained, though: from the first observations, G-1a and G-1b had intermittently spiraled together slightly faster than they should have. The discrepancies had never exceeded one part in a thousand — the waves quickening by an extra nanosecond over a couple of days, every now and then — but when most binary pulsars had orbital decay curves perfect down to the limits of measurement, even nanosecond glitches couldn’t be written off as experimental error or meaningless noise.
Karpal had imagined that this mystery would be among the first to yield to his solitude and dedication, but a plausible explanation had eluded him, year after year. Any sufficiently massive third body, occasionally perturbing the orbit, should have added its own unmistakable signature to the gravitational radiation. Small gas clouds drifting into the system, giving the neutron stars something they could pump into energy-wasting jets, should have caused Lac G-1 to blaze with X-rays. His models had grown wilder and more daring, but all of them had come unstuck from a lack of corroborative evidence, or from sheer implausibility. Energy and momentum couldn’t just be disappearing into the vacuum, but by now he was almost ready to give up trying to balance the books from a hundred light years away.
Almost. With a martyr’s sigh, Karpal touched the highlighted name on the screen, and a plot of the waves from Lacerta for the preceding month appeared.
It was clear at a glance that something was wrong with TERAGO. The hundreds of waves on the screen should have been identical, their peaks at exactly the same height, the signal returning like clockwork to the same maximum strength at the same point on the orbit. Instead, there was a smooth increase in the height of the peaks over the second half of the month — which meant that TERAGO’s calibration must have started drifting. Karpal groaned, and flipped to another periodic source, a binary pulsar in Aquila. There were alternating weak and strong peaks here, since the orbit was highly elliptical, but each set of peaks remained perfectly level. He checked the data for five other sources. There was no sign of calibration drift for any of them.
Baffled, Karpal returned to the Lac G-1 data. He examined the summary above the plot, and sputtered with disbelief. In his absence, the summary claimed, the period of the waves had fallen by almost three minutes. That was ludicrous. Over 28 days, Lac G-1 should have shaved 14.498 microseconds off its hour-long orbit, give or take a few unexplained nanoseconds. There had to be an error in the analysis software; it must have become corrupted, radiation-damaged, a few random bits scrambled by cosmic rays somehow avoiding detection and repair.
He flipped to a plot showing the period of the waves, rather than the waves themselves. It began as it should have, virtually flat at 3627 seconds, then about 12 days into the data set it began to creep down from the horizontal, slowly at first, but at an ever-increasing rate. The last point on the curve was at 3456 seconds. The only way the neutron stars could have moved into a smaller, faster orbit was by losing some of the energy that kept them apart — and to be three minutes faster, instead of 14 microseconds, they would have needed to lose about as much energy in a month as they had in the past million years.
“Bollocks.”
Karpal checked for news from other observatories, but there’d been no activity detected in Lacerta: no X-rays, no UV, no neutrinos, nothing. Lac G-1 had supposedly just shed the energy equivalent of the moon annihilating its antimatter double; even a hundred light years away, that could hardly have passed unnoticed. The missing energy certainly hadn’t gone into gravitational radiation; the apparent power increase there was just 17 percent.
And the period had fallen about 5 percent. Karpal did some calculations in his head, then had the analysis software confirm them in detail. The increasing strength of the gravitational waves was exactly what their decreasing period required. Closer, faster orbits produced stronger gravitational radiation, and this impossible data agreed with the formula, every step of the way. Karpal could not imagine a software error or calibration failure that could mangle the data — for one source only — while magically preserving the correct physical relationship between the power and frequency of the waves.
The signal had to be genuine.
Which meant the energy loss was real.
What was happening out there? Or had happened, a century ago? Karpal looked down a column of figures showing the separation between the neutron stars, as deduced from their orbital period. They’d been moving together steadily at about 48 millimeters a day since observations began. In the preceding twenty-four hours, though, the distance between them had plummeted by over 7,000 kilometers.
Karpal suffered a moment of pure vertiginous panic, but then quickly laughed it off. Such a spectacularly alarming rate of descent couldn’t be sustained for long. Apart from gravitational radiation, there were only two ways to steal energy from a massive cosmic flywheel like this: frictional loss to gas or dust, giving rise to truly astronomical temperatures — ruled out by the absence of UV and X-rays — or the gravitational transfer of energy to another system: some kind of invisible interloper, like a small black hole passing by. But anything capable of absorbing more than a fraction of G-1’s angular momentum would have shown up on TERAGO by now, and anything less substantial would soon be swept away, like a pebble skipping off a grindstone, or blown apart like an exploding centrifuge.
Karpal had the software analyze the latest data from TERAGO’s six nearest detectors, instead of waiting an hour for the full set to arrive. There was still no evidence of any kind of interloper — just the classical signature of a two-body system — but the energy loss showed no sign of halting, or even leveling off.
It was still growing stronger.
How? Karpal suddenly recalled an old idea which he’d briefly considered as an explanation for the minor anomalies. Individual neutrons were always color neutral: they contained one red, one green and one blue quark, tightly bound. But if both cores had “melted” into pools of unconfined quarks able to move about at random, their color would not necessarily average out to neutrality everywhere. Kozuch Theory allowed the perfect symmetry between red, green, and blue quarks to be broken; this was normally an extremely fleeting occurrence, but it was possible that interactions between the neutron stars could stabilize it. Quarks of a certain color could become “locally heavier” in one core, causing them to sink slightly until the attraction of the other quarks buoyed them up; in the other core, quarks of the same color would be lighter, and would rise. Tidal and rotational forces would also come into play.
The separation of color would be minute, but the effects would be dramatic: the two orbiting, polarized cores would generate powerful jets of mesons, which would act to brake the neutron stars’ orbital motion — a kind of nuclear analogue of gravitational radiation, but mediated by the strong force and hence much more energetic. The mesons would decay almost at once into other particles, but this secondary radiation would be very tightly focused, and since the view from the solar system was high above the plane of Lac G-1’s orbit the beams would never be seen head-on. No doubt they’d become spectacularly visible once they slammed into the interstellar medium, but after only 16 days they’d still be traveling through the region of relatively high vacuum that the neutron stars had swept clean over the last few billion years.
The whole system would be like a giant Catherine wheel in reverse, with the fireworks pointing backward, opposing their own spin. But as they bled away the angular momentum that kept them apart, gravity would draw them tighter and they’d whip around faster. The nanosecond glitches in the past might have involved small pools of mobile quarks forming briefly, then freezing back into distinct neutrons again, but once the cores melted completely it would be a runaway process: the closer the neutron stars came to each other, the greater their polarization, the stronger the jets, the more rapid their inward spiral.
Karpal knew that the calculations needed to test this id
He had the analysis software fit a smooth curve through the neutron stars’ declining angular momentum, and extrapolate it into the future. The fall grew faster, gently at first, but it ended in a steep descent. Karpal felt a cool horror wash through him: if this was the ultimate fate of every binary neutron star, it helped make sense of an ancient puzzle. But it was not good news.
For centuries, astronomers had been observing powerful gamma-ray bursts from distant galaxies. If these bursts were due to colliding neutron stars, as suspected, then just before the collision — when the neutron stars were in their closest, fastest orbits — the gravitational waves produced should have been strong enough for TERAGO to pick up over a range of billions of light years. No such waves had ever been detected.
But now it looked as though Lac G-1’s meson jets would succeed in bringing the neutron stars’ orbital motion to a dead halt while they were still tens of thousands of kilometers apart. The Catherine wheel’s fireworks, having finally triumphed, would sputter out, and the end wouldn’t be a frenzied spiral after all, but a calm, graceful dive — generating only a fraction as much gravitational radiation.
Then the two mountain-sized star-heavy nuclei would slam straight together, as if there’d never been a hint of centrifugal force to keep them apart. They’d fall right out of each other’s sky — and the heat of the impact would be felt for a thousand light years.
Karpal dismissed the image angrily. So far, he had nothing but a three-minute anomaly in an orbital period, and a lot of speculation. What was his judgment worth, after nine years of solitude and far too many cosmic rays? He had to get in touch with colleagues in the asteroid belt, show them the data, and talk through the possibilities calmly.
But if he was right? How long did the fleshers have before Lacerta lit up with gamma rays, six thousand times brighter than the sun?
Karpal checked and re-checked the calculations, fitted curves to different variables, tried every known method of extrapolation.
The answer was the same every time.
Four days.
* * *
5
–
Burster
« ^ »
Konishi polis, Earth
24 046 380 271 801 CST
5 April 2996, 21:17:48.955 UT
Yatima floated in the sky above vis homescape, surveying the colossal network that sprawled across the hidden ground as far as ve could see. The structure was ten thousand delta wide and seven thousand high; winding around it was a single, elaborate curve, which looked a bit like one of the roller coaster rides ve’d seen in Carter-Zimmerman — and which ve’d ridden with Blanca and Gabriel, for the visual thrill alone. The “track” here was unsupported, just like the one in C-Z, but it weaved its way through what looked like a riot of scaffolding.
Yatima descended for a closer inspection. The network, the “scaffolding,” was a piece of vis mind, based on a series of snapshots ve’d taken a few megatau before. The space around it glowed softly in a multitude of colors, imbued with an abstract mathematical field, a rule for taking a vector at any point and calculating a number from it, generated by the billions of pulses traveling along the network’s pathways. The curve that wrapped the network encircled every pathway, and by summing the numbers that the field produced from the tangents to the curve along its entire length, Yatima was hoping to measure some subtle but robust properties of the way information flowed through the structure.
It was one more tiny step toward finding an invariant of consciousness: an objective measure of exactly what it was that stayed the same between successive mental states, allowing an ever-changing mind to feel like a single, cohesive entity. The general idea was old, and obvious: short-term memories had to make sense, accumulating smoothly from perceptions and thoughts, then either fading into oblivion or drifting into long-term storage. Formalizing this criterion was difficult, though. A random sequence of mental states wouldn’t feel like anything at all, but neither would many kinds of highly ordered, strongly correlated patterns. Information had to flow in just the right way, each perceptual input and internal feedback gently imprinting itself on the network’s previous state.
When Inoshiro called, Yatima didn’t hesitate to let ver into the scape; it had been far too long since they’d last met. But ve was bemused by the icon that appeared in the air beside ver: Inoshiro’s pewter surface was furrowed and pitted, discolored with corrosion and almost flaking away in places; if not for the signature, Yatima would barely have recognized ver. Ve found the affectation comical, but kept silent; Inoshiro usually viewed the fads to which ve subscribed with appropriate irony, but occasionally ve turned out to be painfully earnest. Yatima had been persona non grata for almost a gigatau after mocking the practice, briefly fashionable across the Coalition, of carrying around a framed portrait of one’s icon “aging” in fast-motion.
Inoshiro said, “What do you know about neutron stars?”
“Not a lot. Why?”
“Gamma-ray bursters?”
“Even less.” Inoshiro looked serious underneath all the rust, so Yatima struggled to remember the details from vis brief flirtation with astrophysics. “I know that gamma rays have been detected from millions of ordinary galaxies — one-off flashes, rarely from the same place twice. The statistics come down to something like one per galaxy per hundred thousand years ... so if they weren’t bright enough to be seen a few billion light years away, we probably wouldn’t even know about them yet. I don’t think the mechanism’s been conclusively established, but I could check in the library —”
“There’s no point; it’s all out-of-date. Something’s happening, outside.”
Yatima listened to the news from the gleisners, not quite believing it, staring past Inoshiro into the scape’s empty sky. Oceans of quarks, invisible meson jets, plummeting neutron stars ... it all sounded terribly quaint and arcane, like some elegant but over-specific theorem at the end of a cul-de-sac.
Inoshiro said bitterly, “The gleisners took forever to convince themselves that the effect was real. We’ve got less than twenty-four hours before the burst hits. A group in Carter-Zimmerman is trying to break into the fleshers’ communications network, but the cable is sheathed with nanoware, it’s defending itself too well. They’re also working on reshaping the satellite footprints, and sending drones straight into the enclaves, but so far —”
Yatima cut in. “I don’t understand. How can the fleshers be in any kind of danger? They might not be as heavily shielded as we are, but they still have the whole atmosphere above them! What portion of the gamma rays will make it to ground level?”
“Almost none. But almost all of them will make it to the lower stratosphere.” An atmospheric specialist in C-Z had modeled the effects in detail; Inoshiro offered an address tag, and Yatima skimmed the file.
The ozone layer over half the planet would be destroyed, immediately. Nitrogen and oxygen in the stratosphere, ionized by the gamma rays, would combine into two hundred billion tons of nitric oxides, thirty thousand times the current amount. This shroud of NOx would not only lower surface temperatures by several degrees, it would keep the ultraviolet window open for a century, catalyzing the destruction of ozone as fast as it reformed.
Eventually, the nitric oxide molecules would drift into the lower atmosphere, where some would split apart into their harmless constituents. The rest — a few billion tons — would fall as acid rain.
Inoshiro continued grimly, “Those predictions all assume a certain total energy for the gamma-ray burst, but that could be as wrong as everything else people thought they knew about Lacerta G-1. At best, the fleshers will need to redesign their w
“That’s terrible.” But Yatima felt verself retreating into a kind of weary resignation. Some fleshers would almost certainly die ... but then, fleshers had always died. They’d had centuries to come into the polises if they’d wanted to leave the precarious hospitality of the physical world behind. Ve glanced down at vis glorious experiment; Inoshiro still hadn’t even given ver a chance to mention it.
“We have to warn them. We have to go back.”
“Go back?” Yatima stared at ver, baffled.
“You and I. We have to go back to Atlanta.”
A tentative image appeared: two fleshers, one of them seated. A man and a woman? Yatima had a feeling ve’d seen them in some artwork of Inoshiro’s, long ago. We have to go back to Atlanta? Was that a line from the same piece? Inoshiro’s slogans all began to sound the same after a while: “We must all go and work in our gardens,” “We have to go back to Atlanta” ...