Free Turn Right At Orion by Mitchell Begelman Page B

chemical elements in various states of excitation and disarray. These intrinsic colors are not to be fiddled with.
    Number 433 in the Stephenson and Sanduleak catalogue had a surprise in store. When measured accurately, the lines had the wrong colors. More frighteningly, the colors changed with time. Enter the Doppler effect, according to which these well-recorded lines are expected to have their original hues only if the luminous
matter is at rest. If it is moving in the direction of the observer, the color will “squeal” toward bluer hues; if away, it will “groan” and turn redder. SS 433 showed three sets of lines—one groaning, one squealing, and one more or less in repose—and therefore seemed to exhibit three states of motion at once. As the headlines said (do they ever lie?), SS 433 was indeed both coming and going, not to mention standing still, and clearly had to be in some terrible sort of trouble.
    Only it wasn’t really in so much trouble. Like the ending of a classical comedy, the resolution of the paradox showed that all was right with the world. The change of hues with time, which (in wilder moments of speculation) had seemed to threaten the foundations of physics, proved to be their salvation. After the lines had been monitored for a few months, a simple pattern emerged. The approach and recession of the “moving lines” oscillated, changing places twice every 164 days. A simple model fit the data perfectly: SS 433 was spraying out a pair of jets in opposite directions, and these rotated with the aforementioned period. The rotation of each jet was a kind of precession, like a searchlight plumbing the sky 20 degrees off the zenith. An early analogy to a rotary lawn sprinkler also proved apt, for analysis of the lines revealed that matter in the jets did not stream out smoothly but rather chugged out impulsively in bullets or blobs of fluid, several per day. Twice per rotation period, the matter in the jets would be moving perpendicular to our line of sight and, according to the classical theory, Should show no Doppler shift. But when these times came, the hues were still shifted to the red. Even this puzzle was quickly resolved. Long ago, the theory of relativity had predicted that time would slow down for a body in motion. Even though it was moving neither toward nor away from us, the matter in the jets was moving, and this dilation of time showed up, exactly as predicted, through a redshift—a slowing down of the frequency of light, Another prediction of Einstein’s theory was confirmed, the steel trap of its validity tightened. And the speed of the matter in the jets could be deduced with precision. It was a quarter of the speed of light.

    While I ran through all this history in my mind, I was steadily approaching SS 433. The smeared-out jet that I had crossed as it plowed through the outer reaches of W50 now seemed to be resolving itself into much finer structure. Each bullet was emitted in a slightly different direction, as the sprinkler head chugged around, and thereafter traveled in a straight line. Far enough away from SS 433, the collective pattern of all these bullets (if they survived) should delineate the surface of a hollow cone. As I crossed back into the jet’s path, I found that the impulse was no longer spread widely but was confined to a conical surface, spread out by about 20 degrees from its axis of symmetry—just as predicted. Closer in, I could see the helical pattern traced by the sequence of bullets emitted during successive rotations, a pattern, that was washed out when viewed on large scales. I recalled how astounded I had been when my radio astronomer colleagues had imaged this very helical pattern, all the way from the 17,000-light-year distance of Earth.
    It was all very familiar, the geometry and motions of the SS 433 jets, and yet the congruence between what I saw and what I expected made it spooky. This level of predictability