Xeelee: Vengeance

by Stephen Baxter

  And so they descended through great fountains, themselves hundreds or thousands of kilometres across, their structure and their cycling flows dimly visible in the neutrino images. Towers taller than worlds, all around them. The temperature slowly clicked up, from a few thousand degrees at the surface, then into the tens of thousands, and then hundreds of thousands. The density quickly increased too, up to that of breathable air – the photosphere, for all its drama and spectacle, was very rarefied – and then beyond.

  The Payne’s speed had been drastically reduced; it would take more than eight hours to pass through this hot density.

  ‘After all that drama at the surface,’ Poole reported, ‘this is kind of calm. I feel sleepy. Nicola is asleep, I think.’

  ‘Payne, Anaxagoras.’ Mitch Gibson’s voice was carried now on modulated neutrino streams sent from Larunda, though there was a backup, a less trusted link passing through the wormhole itself. ‘Sleepy is good. After all, you’re inside a star, dangling at the end of an experimental wormhole technology that is the only thing that is keeping you from flashing to carbonised ash. But it’s working. We can see a healthy fountain of hot gases erupting out of the external portal. The data shows your GUTdrive is functioning perfectly too, and a bleed-off of electromagnetic energy from the drive is deflecting the solar plasma safely away from your hull. Calm is good. Look, take it easy. Accept the process. You’re just a bit of grit in a big pan of boiling water, falling with the currents . . .’

  The pod lurched sideways, with a shove hard enough for Poole to feel, despite the dominant twenty-seven G that kept him pinned to his couch. He didn’t try to fight the restraints that kept his head rigidly still. But he glanced at the monitor fixed on Nicola’s face.

  She was awake, wide-eyed, grinning. Piloting.

  ‘What in Lethe are you doing?’

  ‘Avoiding that. Take a look.’

  And in the monitors, he saw now, a huge form was rising from the depths below. It was like a shining worm, he thought, or a sea snake: silvery it was, in the false-colour neutrino imaging. But this worm had no head or tail: a loop of string, then, rising from some deeper tangle.

  ‘A flux rope,’ he guessed.

  ‘Payne, Anaxagoras. That’s exactly it.’ Gibson sounded excited. ‘Another magnetic phenomenon. A kind of self-reinforcing structure where the field lines gather into a tube, that holds in matter like a hosepipe – but the contained matter is lower density than the average, and so the tube just floats up, up through this zone to the photosphere, and the surface. Buoyancy: simple physics, here in the heart of a star.

  ‘Michael, Nicola did the right thing to get you out of the way. Even if she didn’t need to jerk you around quite so hard.’

  ‘How did you know?’ Poole asked Nicola. ‘I didn’t notice any proximity alarm. And I thought you were asleep.’

  She just grinned again. ‘That’s why I’m here. Anaxagoras, how about a tweak to the mission plan? What if we follow this flux rope all the way down to the tangle it came from? Maybe that will guide us away from any others.’

  Gibson hesitated. ‘Maybe. The modelling is uncertain.’

  ‘I’ll take that as a yes. Do you heroes ever make a decision without your bots’ permission?’ With subtle motions, Nicola worked her controls, and the apparently transparent craft glided alongside the great curving pillar of light. ‘Be more fun to do some steering, anyhow. Let me know when your modelling catches up.’

  Poole snorted. ‘Once a pilot, always a pilot. Maybe you ought to give me a chance to play too.’

  ‘Get some sleep first. You get crusty when you’re tired, Michael.’

  Well, he didn’t sleep any more. And nor did she give him the controls, not through the rest of that phase of the descent.

  All the way to the tachocline.

  Even Nicola instinctively slowed the craft as the next interface approached.

  Eight hours in, they were now more than a hundred thousand kilometres below the Sun’s surface. That was about a quarter the distance from the Earth to the Moon, Poole reflected uneasily. In fact the whole Earth–Moon system could have been contained within the body of the Sun.

  The neutrino imaging showed a kind of carpet beneath them now, a flat-infinite plain in which ropelike structures were embedded, lying roughly parallel. But even as Poole watched he saw those structures move, writhe, as if trying to escape that apparently infinite floor: huge forms, motivated by huge energies. If the granulated surface had seemed infested with life, at least from a distance, and the great bland convection cells by contrast had felt mechanical, a vast engine, here again he had a sense of a kind of quasi-life. He wondered what Jack Grantt would make of such observations.

  ‘Payne, Anaxagoras. OK. You know where you are. This is the outer boundary of the radiation zone. No more atomic matter further in, just the debris of broken atoms: electrons and protons and neutrons and a hell of a lot of scattered radiation. The temperature is already around a million degrees – but the pressure’s not so bad, like a shallow ocean.’

  ‘More flux tubes,’ Poole said. ‘That’s what we’re seeing down there. Correct . . .?’

  He knew the theory. If the convection zone was about steam-engine-era heat flows, the next part of the inner Sun, deeper yet, below this boundary, the tachocline, was like a simple electromagnetic motor.

  The Sun’s magnetic field was created and shaped by rotation. The core and the radiation zone, everything below this layer, rotated with a period of about twenty-five days, like a giant, solid planet. But the layers above the tachocline, the convection zone and photosphere, rotated more slowly, taking around twenty-seven days at the equator, and differentially at other latitudes. With uniform rotation the Sun’s magnetic field would naturally have been like Earth’s, with a north and south pole, and flux lines tamely following lines of longitude, north-south. But the fast-spinning central core screwed up that neat pattern. The magnetic field was everywhere dragged along by the local spin: twenty-five days below the tachocline, twenty-seven days above. So, here at the tachocline, in this zone of shear, the flux lines were pulled west to east, stretched like elastic, wrapping around the tachocline, this spherical surface. Just as Poole saw below him now.

  And every so often one of these great flux tubes, stretched too far, would break away from the tangle, rise up through the convection zone, and ultimately burst out through the photosphere. Thus all of the Sun’s weather – the solar flares, the mass ejections that plagued technological Earth, even the aurorae of the polar regions – was rooted in this tremendous hidden engine.

  Mitch Gibson said, ‘I got experienced physicists up here salivating over the images you are returning. Some of them are complaining that we didn’t timetable in more observations. If only they could see a flux tube actually break away . . .’

  Nicola just ignored that. ‘Continuing with the flight plan.’

  ‘Payne, Anaxagoras. Concur.’

  Now, with great delicacy, Nicola manoeuvred their improvised craft through the tangle of flux ropes. It was a loose array, Poole saw as they descended, but it was three-dimensional and mobile, and he had to applaud, if silently, Nicola’s skill as she guided the vessel through this puzzle – and out, down through that complex roof, and into a featureless glow beneath.

  Featureless save for that steady neutrino-shine coming out of the fusing core itself, far below.

  ‘That was easy,’ Nicola said. ‘You made the simulators too hard, Gibson.’

  ‘Take it up with my boss.’

  ‘I did feel a sideways kick as we passed through that interface and entered the faster-rotating central region. Compensating. And reducing speed . . .’

  Poole knew the drill. Each successive stage of the journey, deeper into ever more challenging environments, was being taken at lesser velocities. It was not anticipated that the Payne could survive an entry into the fusing core its
elf. But still it would take forty-eight more cautious hours before they reached the outer boundary of that zone.

  Unless events intervened.

  This radiation zone might be a physicist’s dream, a realm of enormous congregations of mass and energy. But there was nothing to see but a smooth gas of electrons and protons, immersed in a bath of continually scattered X-ray photons. The complex structure of the convection zone was a memory now; here, nothing changed save for abstract readings of density and temperature and pressure, and the slowly brightening glow in the neutrino imagers of that central core, the star within a star that was the source of all the Sun’s heat and radiation. It was, Poole thought, like falling down the slope of some mathematician’s abstracted graph.

  Time seemed to pass even more slowly.

  He tried to eat – meaning, taking solid food as opposed to the nutrients that were continually pumped into his system. The psychologists on Larunda had advised it would be good for his morale. But, despite exoskeletal support, the effort made his jaw muscles ache, the heavy gravity fighting him all the way, and he gave up.

  Nicola was silent for such long periods it was hard to tell if she slept or not. Even Mitch Gibson went off air for a time, taking his own biological downtime.

  And with nobody speaking to him, Poole, lost in his own thoughts, in an environment of sensory deprivation, actually grew bored. He couldn’t always tell if he was asleep or awake.

  Until Nicola murmured, ‘Michael. We found something.’

  19

  Poole took one look out of the faux-transparent hull.

  Then he looked away. He studied his control panels, trying to get his bearings.

  He must have slept, after all. They had been passing through the radiation zone for nearly two days – only another few hours before they were due to reach the boundary of the core, and would have to turn back. They were just a third of the solar radius out from the centre now, with nearly five hundred thousand kilometres of starstuff over their heads. The view outside was empty, with only that still-brighter core glow from beneath showing in the neutrino monitors.

  Empty, save for the fish that were swimming past the windows.

  ‘Fish?’ Nicola asked.

  Poole hadn’t realised he had spoken out loud. He looked again.

  Fish, yes, they were like flatfish, or rays: roughly circular forms, thicker at the middle, thinner at the edges – lenticular – pale, greyish, translucent, almost transparent in the imagers’ rendering. But big, each maybe fifty metres across. Individuals were difficult to make out, such was the size and density of the flock.

  Swimming past his window. In the heart of the Sun.

  ‘Not a flock,’ he said, almost to himself. ‘A school? A school of fish. Yes. But, fish inside the Sun?’

  ‘Payne, Anaxagoras. Stay calm down there.’

  ‘Easy for you to say,’ Nicola snapped.

  ‘They’re all around you. As soon as you were spotted by outliers, this flock—’

  ‘School, Mitch,’ Poole said. ‘School.’

  ‘Whatever. They rose up in a big cloud, from deeper in the core. We can’t make out individuals well from up here – we can’t even see the lower edge of the cloud, the school. But now we know what to look for, we can tell they’re there. All around the core, Michael. A shell of them. Incredible. A feature nobody saw before.’

  ‘Not a feature,’ Nicola said scornfully. ‘What kind of word is that? I don’t know if Michael’s “school” is right. But they’re alive, Gibson. Alive, inside the Sun. And they are swimming around in this high-energy gloop of protons and electrons like it was thin air.’

  ‘To them, it is,’ Gibson said. ‘We can tell what those things are made of—’

  ‘Dark matter,’ Poole said, guessing wildly. ‘Correct?’

  ‘You got it,’ Gibson said, sounding surprised. ‘That’s what our tame physicists are saying. Dark matter only interacts with our kind of matter – baryonic matter – through gravity. On the large scale, dark matter is the stuff that gives the universe its structure, of galaxies and clusters of galaxies, and superclusters of clusters . . . And now, on the small scale, here it is gathered in the heart of a star. Nuclear, electromagnetic forces don’t mean a thing to dark matter. So here are these objects, swimming through this super-hot electron-proton plasma as if it didn’t exist. In fact our imagers can only see them by their very occasional interactions of the particles they’re composed of with normal matter, and some very subtle gravitational lensing, a deflection of the neutrino streams . . .’

  Nicola glanced over. ‘That’s surprisingly acute for you, Poole.’

  ‘Well, what else could pass through this stuff like it was mist?’

  ‘I can’t believe nobody knew this was here before. Somebody must have guessed.’

  Gibson hesitated, evidently consulting. ‘Payne, Anaxagoras. Quite right, Nicola. There were speculations, at least. A dark matter, umm, cloud, was the best explanation of certain anomalies about the heat distribution in the centre of the Sun. First detected millennia ago, actually. More recently we’ve detected peculiar flows of helium from the outer layers into the core. You understand that the Sun is around a quarter helium by mass anyhow, and that excess helium is “ash” created by the core fusion processes. So it’s as if somebody was shovelling ash onto a burning fire . . . It was one of the goals of the original Sun Probe project to check all this out. Nobody expected this, though.’

  ‘Life, you mean?’

  ‘Well, let’s not jump to conclusions—’

  Nicola seemed uncharacteristically thoughtful. ‘Maybe we shouldn’t be surprised. Isn’t that what they used to say about the old planetary explorers? Everywhere the humans went, they found life . . . But what do these dark matter fish eat? Maybe they consume Sun-core fusion energy – no, it can’t be that; they don’t interact with electromagnetic fields, do they? Maybe it’s something to do with the gravity. Maybe the hearts of stars are breeding grounds for them, wherever the gravity wells are deep enough for them to gather, and they feed off gravitational waves, and shovel helium into the cores for fun . . . Uncle Jack would love this, Michael.’

  Poole said now, ‘One question. Did these – fish – come here with the Cache?’

  ‘Payne, Anaxagoras. We don’t believe so. My guys are rechecking our old records. We weren’t specifically looking for dark matter entities, but the scans should have shown up any such change. Best guess is that these fish of yours have been here a long time, Michael.’

  Nicola said softly, ‘But that hasn’t.’ She pointed.

  It hovered beyond the window. Suddenly there.

  Black wings sweeping behind a blocky body, and its blunt head-like prow squarely facing the Payne. Where the dark matter fish were pale, translucent, this was solid, black in the neutrino imaging. And where the fish looked blurred, soft-edged, this was hard, sharp.

  The sycamore seed.

  ‘Wow,’ Nicola said. ‘Suddenly this scow seems fragile.’

  ‘We didn’t see it coming,’ Gibson admitted. ‘We’re tracing it back – it must have moved through the solar medium at a murderous pace.’

  ‘No creeping around like us, then.’

  ‘No, Nicola. As far as we can tell it seems to have been inspecting these flocks of dark matter fish. Orbiting the Sun’s core with them . . . Then, suddenly, it came for you. Your craft is trying to talk to it, by the way.’

  ‘What?’

  ‘One of the mission objectives has been to attempt to contact the intruder, if you ever got close enough. So you have the systems to fulfil that.’

  Nicola laughed. ‘Are we counting out the primes one neutrino pulse at a time?’

  ‘You’re not entirely wrong.’

  Poole couldn’t take his eyes off that blunt, powerful form. He struggled against the ferocious gravity, scarcely lessened even thoug
h they were so deep in the Sun’s substance; he longed to stand, to face this thing on his feet, but he could not. ‘Who are you? Why are you here? Are you studying these fish creatures? What in Lethe do you want?’

  Nicola said, ‘Actually I think I know what it wants, right now anyhow. Look at this, Michael Poole.’

  A Virtual reconstruction congealed in the air before him. Poole saw a small spacecraft embedded inside an electric-blue tetrahedral frame, facing another artefact, much larger: black as night despite the torrent of light around it, a compact body with swept-back wings.

  ‘That’s us,’ Nicola said, pointing. ‘Us and the sycamore seed. Or, to be precise, here’s us.’

  The spacecraft shape dissolved, a glimpse of a complex interior, burning away. Two figures were left, seated on nothing, floating in the glowing air. Facing the sycamore seed.

  ‘Us. Me on the left, you on the right. Bye, Nicola.’

  The left-hand figure dissolved in a spray of pixels.

  Leaving the sycamore seed, and that right-hand figure. Facing each other, head on.

  ‘Lethe, Michael. It couldn’t be clearer. I’ve set up some precision measurement routines . . . Somehow the sycamore seed knew you were in here. And it has come to rest right in front of you. Right in front. You’re on its axis of symmetry. Michael, the sycamore seed isn’t just here for these dark matter fish. It’s here for you.’

  With an angry gesture, he dismissed the Virtual.

  Outside, still the sycamore seed lingered. Then, abruptly, without warning, it did a kind of back-flip, and shot away, out of sight.

  For a long interval there was silence.

  Poole said, ‘We’ve seen what we came for. Get us out of here.’

  For once Nicola didn’t answer back. With tentative high-gravity gestures she worked her controls.

  The school of dark matter fish followed the Payne for a while, as it rose back up into the glowing sky from which it had descended. Then they turned away, returning to their own endless circling of the core of the Sun.