Turn Right At Orion

by Mitchell Begelman

  I followed the stream back toward its source. Subconsciously, I must have expected to revisit one of the dramatic environments of my earlier travels—a jet from a black hole or neutron star binary, perhaps—despite the fact that this stream of gas was traveling a hundred times slower, merely a few hundred kilometers per second. It was a bigger surprise than it should have been, therefore, to find that I was being led back to an object very similar to the one I had just left. As I approached, I saw the familiar thin, dusty disk surrounding a glowing sphere. This protostar seemed to have evolved to a slightly more advanced stage than its compatriot. The contracting envelope had been, more or less, entirety dispersed, the sphere was slightly smaller and hotter, and the disk was just a bit more spread out.

  With difficulty, I could trace the jet nearly all the way to the protostar. It was faint here, the bright splotches not having formed this close to the jet’s source. The jet seemed to emerge from the very innermost regions of the disk, just outside the point where it brushed the globe of the newly radiant star. Although strong outward propulsion dominated its motion, the helical shape of the magnetic streamers that embraced it revealed that the jet also swirled about its axis. This was not surprising, given the jet’s origin in the rapidly rotating disk. What did surprise me was to see, once again, the streamers of magnetic field, this time outlining the jet like a candy cane. The swirling jet seemed to be wrapping lines of magnetic force tightly about itself. Or was it the other way around? I suspected that it was the jet that was doing the bidding of the magnetic field. The magnetic field here was strong, much stronger than the field of the protostar I had visited previously. Probably it had been amplified by the rotation of the disk, which had become hot enough to hold onto its magnetic field once again. As I had found in my earlier travels, energy was fungible: It could slip just as easily from its rotational form to its magnetic form as from rotation to heat or from heat to light. The field was wound up like a mainspring, and I could sense its tension as it struggled to unleash its pent-up energy—to convert itself back to the energy of motion. But magnetism’s peculiar form of tension would not permit it to lash out equally in all directions. As it propelled the jet forward, the helical turns of magnetic field squeezed inward toward the common axis, seeming to suffocate the jet like a boa constrictor. This seemed likely to be the cause of the jet’s slenderness, yet the constrictive and propulsive forces were not finely balanced. The jet lurched forward in spurts, its direction wavering and its degree of focus equally unsteady. As I peered outward along the jet, in the dim distance I could make out these spurts colliding and shocking, to create the first of the bright splotches that had given the jet away.

  As I pulled farther from the center of the disk, the scene became much more familiar. If the magnetic field had seemed combed out and orderly during the early stages of the previous protostar’s contraction, by this stage in the evolution of the present protostar it had assumed a disorderly, chaotic structure. Flares erupted from this disk, reminiscent of the ones I had seen in the accretion disks of Cygnus X-1 and SS 433. Although, the most powerful and fastest expulsions of matter came from the center of the disk, where the effects of both gravity and rotation were most pronounced, outbursts were occurring all along the surface of the disk. How strange to see the fireworks that I had come to associate with black holes and neutron stars repeated, in milder form, as gravity and rotation struggled over a mundane prize like a young star.

  As had been almost universally the case whenever I encountered a new phenomenon, this protostar’s jet was no freak. As I looked about me, I could now recognize dozens of trains of these shock-splotches strewn about the sky, a network of shafts like so many pick-up sticks. It was no surprise that jets came in symmetrical pairs, emerging in opposite directions along the axis of rotation of each disk. It seemed that virtually every newly formed star, heavy or light, produced a pair of jets. If I hadn’t noticed a jet emanating from the first protostar I had visited, it was only for want of bright tracers. Had I accidentally wandered into the beam, I surely would have been apprised, rudely, of the jet’s existence. Now, peering toward that first protostar from a distance, I could see its train of aligned shock waves clearly.

  I gradually began to pull away from the Orion region. As my field of view expanded, so did my understanding. I realized that Orion was much more than a backdrop for its main attractions, the Trapezium and the Nebula. In every quarter it was a beehive of activity: stars forming everywhere, their jets, winds, and radiant output churning up the molecular gas, modifying their environments, creating the conditions for further creation. Orion was a venue different from the others I had visited. The Crabs, the cannibalistic black holes Cygnus X-1 and (perhaps) SS 433, even the Galactic Center—they were all definite places, coordinates one could dial into one’s navigation system. When I set my sight on Orion, I had had in mind an excursion to—where? The Nebula? That insubstantial glowing sheet? The Trapezium? Just those four stars that happen to be this week’s centerpiece? Next week (of course I mean next millennium, or sometime in the next million years) some other stars will have stolen the spotlight, illuminating this ponderous mass of dust and molecules from a different angle. And someday this entire complex of molecular clouds will be gone, and a new Orion will shine somewhere else in the Galaxy.

  At this seemingly unexceptional moment, my perspective on the voyage suddenly changed. One cannot regard Orion as a “place” to visit, any more than one can regard “North America” as the destination for a two-week vacation. Suddenly, I saw my trip not as a sequence of visits to curiosities, each with its set of mechanisms—those of gravity, motion, and equilibrium—but as an exploration of process. Gravity drew matter in toward the center of a galaxy. The Crab pulsar was locked in rigor mortis in the aftermath of a star’s violent death. And Orion’s symbolism was the sweetest of all I had seen so far: The birth of structure from chaos.

  I cannot explain why, but my attention was suddenly diverted to an unimposing swarm of condensations. They were like so many others I had seen, an unassuming cluster of disks, but there was something different about them. I interrupted my departure, wheeled about, and plunged back into the molecular cloud. It turned out that I was responding to the call of the wild.

  17

  The Dust Storm

  During one of my journeys before leaving Earth I encountered a sandstorm. I am sure it was not one of the more extreme versions of this phenomenon, but it was frightening enough, all the same. A sandstorm terrifies by choking all of one’s senses. Smell and taste become indistinguishable and then disappear altogether. Sight, of course, is useless—better to protect one’s eyes as best one can. The whir of sandblasting against car, fencepost, and clothing provides a percussion that accompanies the droning of the wind, masking all sounds that carry useful information. And touch signals only pulverized grit getting into everything.

  Although I was not exposed to the (far harsher) elements outside my craft as I traveled into the disk, the environment in which I now found myself had similar psychological effects. If anything, it was even more disorienting. There was no ground beneath my craft, no porch railing to hang on to. A uniform blankness extended in all directions. I had lost my bearings the moment I descended into the dense layers of swirling dust, losing sight of the Trapezium’s now familiar stars. From afar, the disk had seemed so intriguing, a dark teardrop silhouetted against the pink of the nebula, near the wall of the Trapezium’s cavity. The blunt end of the teardrop faced the Trapezium’s brightest star and was clearly being shaped by its windy punch. On the leeward side, the stream of dust being scoured off tapered down nearly to a point. The wind’s impact was doing its best to decimate this dusty wafer, but I could easily see that its effects were destined to be superficial. The disk had already shrunk under its own gravity to such a degree that it was nearly impervious even to the buffeting of a hot star’s wind.

  It had beckoned as a respite from the stark glare of the brightest of the Trapezium
stars, and that, in a sense, it was. As soon as I entered its outer fringes, the harsh light mellowed. First I lost the ultraviolet glare—a most welcome relief. Then the blues went, leaving a yellowish cast. This steadily reddened as I sank deeper toward the tight plane along which most of the dust was concentrated. I knew that this disk was orbiting a newly formed star; it was in fact the debris left over from the star’s formation. This was not a massive star, like the Trapezium behemoths, but one that would probably come to resemble the Sun when it reached maturity. The star poked above the disk—indeed, it had already cleared a hole around itself—and I had a chance to study it as I approached. From the star’s color, its size, and the intensity of its light, I could surmise that it was still heating up, which meant that it was not through shrinking down toward its final size. But neither was it falling in on itself. To support its weight and slow its shrinkage to an imperceptible rate, the temperature in the center of its core must already have risen above 10 million degrees. This meant that its nuclear-powered furnace had sputtered into action and was ramping up to the level at which it could sustain the full-fledged star for billions of years. It was already a self-sufficient body; the disk seemed superfluous.

  Yet it was the disk, not the fledgling star, that had drawn me here. Such dusty disks of debris contained the only possible raw material from which planets could have formed. I needed to see the process for myself, and preferably around a star with which I could identify—I mean, of course, a star like the Sun. Witnessing stars themselves being born had extended my appreciation of phenomena that I had encountered elsewhere. The relationships were forming themselves into a mantra in my thoughts. Gravity’s inevitable tendency was to draw matter toward a common center. Heat and spin hampered such condensation, but when these were disposed of—often (I had learned) through spectacular jets of gas or the springy dynamics of magnetic fields, or both—gravity would nearly always win. Under much more extreme conditions, near black holes, I had seen how gravity could endow matter with violent motions and unleash torrents of energy. If that had seemed to symbolize a destructive side of gravitational force, then lately, in the stellar nurseries of Orion, I had discovered its creative side. Gravity liked texture. It was inclined to produce interesting patterns (the spiral arms of the Milky Way came to mind) and to create glowing new structures from featureless lumps of gas.

  But planet formation seemed different. It had to occur after the star had formed, or at least late in the star’s process of condensation. Planets were, after all, mere afterthoughts to stars, leftovers that had congealed into bodies that sometimes—at least once, but who knows how commonly—hosted life. Were they really so different from the little cinnamon crusts that my mother had baked from leftover strips of dough when the main event—the pie—was cooling? By that reckoning, planets could seem so inconsequential. Yet I remembered those crusts as the real treat on baking days. Little as they represented in terms of matter and energy, planets would always be regarded as special, even by the most hard-nosed astrophysicist. They were irresistible objects of intrigue mainly because they reminded us of home—they were all potential habitats. But from a different perspective, they were special in their own right. One could think of planets as distillates of the rarest elements, of a purity not found elsewhere in the cosmos. Hydrogen and helium having been boiled off, and metallic solids separated from brittle ceramic and glassy minerals, the construction of a planet simulated the archetypal labors of smelting, metalworking, and pottery. Amid the unyielding and often crude chains of events that shaped the Universe, it seemed surprising that structures so delicate should emerge spontaneously. Even planets like Jupiter, whose hydrogen-rich sheath and odd luminous emanations made many astronomers consider it partway toward being a star, had its rocky core.

  The disk I was exploring seemed very far from evoking the comforting terra firma of a planetary surface, however. If ever one sought a visceral representation of chaos, filled with neither darkness nor light, lacking perceptible structure and orientation, the deep interior of such a disk would be a good candidate. I wondered whether the author of Genesis had preceded me to this spot. How does one go from this featureless morass to the rust-red globe of a Mars, a candy-striped Jupiter with its Great Red Hurricane, or a blue- and white-speckled Earth? I thought of the punch line to that ancient joke about asking directions in the countryside: “You can’t get there from here.” But clearly you could, and I needed to find out how.

  Objectively, the scene was not particularly violent, at least by the standards of my previous travels. If anything, the calm quality of this disk added to my unease. I had earlier lost sight of the star at the center of the disk, its location finally marked by a fading infrared glow that was my last positional point of reference. I guided Rocinante into the dust plane and brought my craft as nearly as possible into synchronization with the orbital motion of the dust particles. This meant that I was orbiting the central star at a few kilometers per second, but my orbital motion was imperceptible because the dust that surrounded me was orbiting at exactly the same speed. The individual grains were not stationary with respect to my position, however. From my moving platform, I perceived them to be darting in completely random directions at about the speed of a fast-moving car. Though this was little more than a thousandth of the orbital speed, and was completely negligible compared to the speeds to which I had become accustomed in my travels, it was shocking to see particles of macroscopic size, that one could scoop up and hold in one’s (well-gloved) hand, barreling along in this way. It was as though I were back in the sandstorm, with the grit particles moving around at high speeds but with no wind to drive them in a fixed direction.

  What struck me as most strange was that I was suddenly immersed in an environment that was comprehensible to human senses. Everywhere else I had encountered bodies so large (or atoms so small) and speeds so incomprehensible that I had been forced to abstract an idea of their dimensions through the use of my instruments or the conscious interpretation of my observations. I knew that the atoms of air at room temperature were moving 10 times faster than these grains, but because I couldn’t see the atoms I had never had to address the reality of that motion. Here I could sense directly what was happening, to the extent of having to put up with the racket of these tiny grains striking Rocinante’s windows dozens of times per second. They made the same kind of rattling noise that had driven me to distraction during that sandstorm many years ago. And through the windows I could see these particles flying at me from all directions, like flakes in an infernal snowstorm. I found it curious that a terrestrial sandstorm would linger in my memory as having temporarily robbed me of my senses, whereas its cosmic counterpart would suddenly restore them to relevance. I took this as a preliminary, indirect sign that perhaps some order amenable to life could emerge from this formless debris.

  Not that I was surprised to see the grains in random motion. I reckoned there was enough unconsolidated dust to construct, maybe, a thousand Earths, spread in a disk that extended out from the central star to at least 100 times the size of the Earth’s orbit around the Sun. The dust layer was thin, but not infinitely so. Most of the dust was concentrated along a sheet that was about 1000 times thinner than it was broad. Yet the breadth of the sheet was so great that it was still thick enough to hold a thousand Earths laid side by side. The disk’s finite thickness went hand in hand with the random motions that had announced themselves so annoyingly along Rocinante’s ceramic skin. The motions of the grains were exactly analogous to the motions of molecules that give pressure to a gas. If this pressure did not exist, the gravitational attraction of the central star would draw a gaseous disk down to a plane of paper thinness, and the same thing would happen to a disk of dust if the particles did not have some random motions superimposed on their orbital circulation. The average speed of the grains was linked to the thickness of the disk via the star’s gravitational attraction, just as the speeds of gaseous atoms had been in proportion to the thickness
of the disk I had visited in Cygnus X-1. I was comforted to find that this dust disk was a good facsimile of the gaseous disks I had seen time and again, only this time executed in the medium of pulverized stone.

  What caused the grains to dance continually? Unlike the disks of gas I had visited before, there were no eruptions of magnetic flares, no bursts of radiation remotely intense enough to stir up these heavy particles of grit. Still, I surmised that this thickening was not accidental. Had the disk been thinner, the dust particles pressed more closely together, the gravitational attractions of the dust grains for one another would have partially overwhelmed their organized attraction to the central star. Once this happened, the smooth structure of the disk would dissolve into striations, braids, and swarms of dust that would not stand still. All of this activity would amount to a stirring action, which would give the dust even more random motions than I had measured. Thus it was gravity that must have stirred up the grains. just enough stirring, and the dust’s self-attraction would balance the pull of the star. It seemed like a new kind of equilibrium, one in which two sources of gravitational attraction—dust for dust versus star for dust—had achieved a delicate balance. But I quickly realized that it wasn’t completely unfamiliar. A similar competition, in which stars played the role of dust grains and the Galaxy as a whole served as the central star, gave rise to the spiral waves that decorated the Milky Way. I was pleased to see the connection, but a little wistful that true novelties were becoming rarer as my travels continued.