Turn Right At Orion (9 page)

Through the light fog I could see the stream of gas crossing the gap between the tortured star and the accretion disk. It was more ragged and active than the stream in Cygnus X-1, and it looked like some of the debris—though not all—was being torn off its margins. Compared to this gushing firehose, the stream feeding the disk in Cygnus X-1 looked tame; thus it came as no surprise to me when I later deduced that matter was flowing
across to SS 433's cauldron at 100 times the rate at which mass was being transferred to Cygnus X-1. I peered ahead to see whether I could spot the hole at the center of the disk, if indeed there was a black hole there, but all I saw was an X-ray/ultraviolet shimmer behind a gauzy screen.

With difficulty I descended to trace the lay of the disk and saw that, unlike the swirling platter in Cygnus X-1, it was not flat. A rolling, warp, its spiral twist sweeping one turn around the center and coming out to envelop
Rocinante
as though in the trough of a gigantic sea swell, disoriented me and made me slightly woozy. The disk was apparently wobbling like a top, guiding the 164-day precession march of the jets, but for now the reasons eluded me. I cautiously crept inward, but the roller-coaster scene had triggered a panic attack that I had difficulty controlling. What if I should encounter those sickening tidal forces again? Still I inched toward the center of the disk, jaw clenched and palms moist. At 10,000 kilometers from the center I felt the first twinges of tidal stretching—and froze. I could go no farther.

Neither could I see any farther. The churning gas just in front of me became so dense that it formed a glowing wall, its outer boundary so indistinct that it seemed diffuse and opaque at the same time. There was no disk from here on in. What had been a thin orbiting structure (its warp superimposed on it like the warp in a potato chip) had ballooned into an immense quasi-spherical bulge, as though some force from within were trying to blow it apart. As if to underline its dispersive tendencies, this gaseous globe expelled a good fraction of the powerful wind and debris that I had puzzled over earlier. But the force I was familiar with, gravity, could not be doing this: Gravity was always attractive! The bulge hid the center from further scrutiny, and I had to pull up and creep along the diffuse surface to avoid flying blind. I noted that the bulge still retained a great deal of the disk's rotation and thought that maybe, if I headed for the rotation axis, the flow would open up into an evacuated funnel, like a whirlpool in the sea or (more prosaically) in the water going
down a drain. But like the maelstroms that wreck ships in classical sagas, this one had its own version of a waterspout shooting up through the center: the jet. As I came over the lip and one of the rotational poles came into view, I was blown away (almost literally) by the spectacle of this massive ejection. The jet wasn't emerging calmly through an evacuated funnel lined with smoothly rotating gas; it was blasting its way through with a great deal of violence. True, the centrifugal force of rotation created a preferred alignment for the jet's path, but once it had found the weak spot, the jet forced the gas aside, opening up a clear channel by its sheer impact. Through this channel a searchlight beam of X-rays and ultraviolet rays accompanied the jet out into open space, and the matter in the jet fluoresced in the glow of its own sheath of radiation. Even the protons and neutrons inside the nuclei of some of the atoms were disturbed by this tremendous agitation and emitted a spectrum of gamma rays. With atoms knocking together at a quarter of the speed of light, this was not hard to comprehend.

I tallied up the matter flying away from this object, in all its forms—hot wind, debris, fast jets—and came to a startling conclusion. SS 433's intense gravitation was extracting from its companion 100 times more matter every second than was disappearing into Cygnus X-1's maw. But instead of swallowing this matter, SS 433 was shooting most of it back out into space. Why?

I saw how such an imbalance
might
come about. As matter sinks deep into the gravitational field, it acquires a lot of energy. First comes motion, as the matter is accelerated by the gravitational pull, then perhaps heat, and then radiation. I had already worked out this chain of energy flow for Cygnus X-1, But I hadn't taken into account the many ways in which energy can be transported from one place to another. Heat is conducted from high temperature to low; radiation leaks out into dark space; stretchy coils of magnetic field set widely separated gaseous filaments in motion; hot cells of turbulent fluid boil up through a cooler atmosphere. In each case, energy is deposited somewhere
other than the place in which it was liberated, and deposition of energy can lead to motion where it is least expected. The pressure of radiation forcing its way through from below was perpetually blowing apart the shroud of SS 433, puffing it up from within until it released its wind and debris. I was less certain what mechanism propelled the jets, because their origin was hidden—but I now understood that means, opportunity, and perhaps motive could readily exist for this seemingly illegal escape from the clutches of a black hole. Whatever the mechanism, it wouldn't take much for a small amount of matter, skimming just outside the black hole, to unleash enough power to blow away a much larger amount of matter that never even got close.

This all seemed to make sense, but did it require that there actually be a black hole at the center of SS 433? I had read somewhere that a debate still raged over whether the enshrouded collapsed star was a neutron star or a black hole, because attempts to estimate its mass had been inconclusive. I suppose I could have solved that problem on the spot with a few measurements of speed and distance for my freely falling craft or with precise orbital measurements of the two stellar companions. But I was too preoccupied by what I had just learned to worry about such refinements. Black hole or neutron star, I doubted that it would make much difference to the outcome. A neutron star's gravity had to be nearly as strong as that of a black hole, and it was the competition between gravity and motion, not any special properties of the gravitating body, that was in question.

What I now understood was that gravity and motion were not always so finely tuned. I had seen some examples of an exquisite balance—were they the exception? My thoughts returned to the steady march of the stars orbiting the Galaxy, in nearly perfect circular orbits. Even the slight imbalances that led to spiral arms—in which gravity wins a little bit each time a star slows down as it encounters one of those interstellar traffic jams—had a certain grace and delicacy about them. The tidal disruption of a star by a black hole was more heavy-handed and really quite violent, but at least it was a fleeting event that occurred and then
was over. Except for a modest escape of some of the accreting gas, Cygnus X-1 made a clean trade of matter for energy. Yet the violent disequilibrium of SS 433 seemed to be a chronic condition. Did the black hole (or neutron star) not know its own strength? Did it grasp the substance it sought to incorporate with such vehemence that it overshot and flung most of it away?

I knew that gravity and motion were not really out of control. All of this had to be predictable. It was just shocking to see matter flout such a strong gravitational field. And SS 433 was not unique. There were episodic jet-emitting black holes that produced surges every so often, for reasons unknown. In these cases, the entire insides of a disk would suddenly drain toward the black hole (like the extremely low tide that precedes a tsunami), only to resurge in the form of jets shooting outward along the rotational axis at speeds even closer to the speed of light than SS 433's jets. Apparently, black holes did not exist simply to attract and devour, as popular literature would have it. Surely this would be the impulse of gravity, left to its own devices. But I saw that when combined with the curious and often contrary properties of matter—its momentum, pressure, radiation, and magnetic fields—gravity could often repel matter or expel it, or even compel it to whirl with wild abandon. Yet in the disk of the Milky Way, the departures from regularity were subtle. Somehow gravity was able to play with motion to achieve a nearly perfect balance. I knew, of course, that the same thing, on a microscopic scale, prevented the Sun and all stars from collapsing in on themselves, at least for a while.

I had a choice to make. Should I seek out examples of ever more violent and contrary phenomena driven by gravitation? I felt naturally attracted to the dramatic, the surprising, and the exotic, and at first this seemed to argue for undertaking the quest after super-fast jets. Probably I was also attracted to the idea that jets mounted a heroic resistance to authority: the victory of the underdog in standing up to gravity. But there was also a kind of tension and high drama in the challenge I finally selected—the quest for equilibrium. For I knew that equilibrium
was not just stasis; it was a standoff in the fierce competition between huge forces of attraction and equally huge forces of resistance. When expressed in these terms, even the benign equilibrium of the smiling Sun seemed to survive in a kind of “balance of terror.” One uncompensated deviation on either side of the fulcrum could lead to disaster.

As I debated with myself, I began to pull away from the SS 433 system, not really sure of my next destination. One more feature of SS 433 nagged at me. What caused the disk to warp? This really didn't seem to make sense. The matter flowing across from SS 433's companion star arrived imprinted with the spin of the binary's orbit. If anything should have been a gyroscope, retaining its orientation as the world around it turned topsy-turvy, it is that disk. Could this too be a symptom of the general failure to attain equilibrium, with a portion of that redeposited energy—some radiative, magnetic, or thermal torque—twisting the disk away from its preferred direction? Remarkably, even that seemed possible. And it also seemed possible in Cygnus X-1, whose disk I had perceived as being so flat. Hadn't I read somewhere that it, too, showed some evidence of a wobble? Maybe, in my naïveté, I had wished it flat. Knowing now that the interactions between gravity and matter could be more complex than I had ever imagined, I turned my attention to the next phase of my exploration, the quest for a rock-steady truce between gravity and matter.

It struck me, as I accelerated away from SS 433 and prepared for hibernation, that more than 65,000 years had passed on Earth since my departure. In all likelihood, the scientific conundrums I was confronting—so far, with mixed success—had long ago been resolved by more ingenious if less direct methods . . . assuming that science was still practiced at home. The goals, norms, and technologies of civilization must have been altered far beyond recognition by now. How many other travelers, or colonies of travelers, from Earth might now be sharing interstellar space with me? Or had physical space travel been a transient fashion, quickly superseded by something more efficient, perhaps the transmission of some digital “essence” of intelligence and personality without the need for an accompanying organic receptacle?

The passage of time might be quite irrelevant to such a virtual being. I, on the other hand, had to worry about aging. As I intimated earlier, I address this problem by manipulating the passage of my time. There is nothing mysterious about this. I exploit the most elementary consequence of Einstein's special theory of relativity, the effect known as time dilation. As viewed from the Earth or from nearly any other observing platform in the Galaxy, time flows more slowly for me, simply by virtue of my high speed. The astute reader might have noticed my allusion
to the phenomenon of time dilation when I explained how SS 433's motions had been deduced using Doppler shifts. To show why time dilation occurs and how to exploit it, I first need to explain a little bit more about the principles of relativity.

People had known since the seventeenth century that light travels with a finite speed, about 300,000 kilometers per second. It had seemed self-evident that if you could travel at, say, 150,000 kilometers per second toward the source of a light beam, then you should measure its speed as 300,000 + 150,000 = 450,000 kilometers per second. After all, in normal experience speed is relative: When you pass a car on the freeway, it actually seems to be going backwards, relative to you. However, in 1905 Albert Einstein realized that speeds close to the speed of light behave differently. For example, if a truck is barreling toward you at 200,000 kilometers per second (two-thirds the speed of light) and you are suicidal and head toward it at 100,000 km/s (one-third the speed of slight), then the two speeds do not add up to the speed of light, as a simple sum would suggest. Instead you will find yourself closing in on the truck at only
, or 82 percent, of the speed of light. This is because speeds become “less relative”—they do not simply add up—as they approach light speed. The speed of a light beam is not relative at all; it has exactly the same value, no matter how fast you are going and in what direction. What Einstein showed is that space and time, not speed, are the fundamentally relative quantities. Space and time become distorted—stretched or compressed—according to your state of motion, in such a way that all observers will agree on the value of the speed of light.