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in a gas is the hallmark of “temperature.” In Earth’s atmosphere, this kind of sharing occurs so instantaneously that one can be sure an average oxygen molecule will carry the same amount of energy as the average nitrogen molecule and will therefore be moving with only 93 percent of the nitrogen molecule’s speed (the square root of ⅞, which is the inverse ratio of their molecular weights). But here, I found that the electrons had wildly different—usually lower—energies from the protons, despite the fact
that all the particle varieties were mixed together. To make matters even more confusing, I found that a small fraction of the electrons had vastly higher energies than the protons.
    This weird distribution of energies went hand in hand with the weird spectrum of radiation. I pictured the glowing heat-shield of my craft on the innumerable occasions when I had re-entered the Earth’s atmosphere in early tests. That progression of colors—red, then orange, yellow, and blue-white—is burned into the visual memory of any habitual space traveler, as is its significance: It tells you the heat-shield is getting hotter. Any solid substance glows with a fixed shade of color that depends on its temperature. The same goes for dense gases, like the atmospheres of these blue stars in the Milky Way’s center (20,000–30,000 degrees), the atmosphere of the Sun (5800°C), and even the Earth’s atmosphere (glowing in the infrared at about 300°C above absolute zero). But the gas surrounding the Milky Way’s central black hole is so transparent, so tenuous, and so “non-thermal” that its “color” seems to have nothing to do with its temperature. Or maybe it is more precise to say that it has no well-defined color. Or, if you will, it is so blessed with electromagnetic radiation of all kinds that it can’t decide which color to be.
    I followed this multicolored whiff of glowing gas as far I could toward its doom. In the interest of safety, I took care not to venture below the 24-million-kilometer “orbit of instability.” This is not the horizon of the black hole, below which there is no way to escape—that’s at 8 million kilometers. But according to Einstein’s general theory of relativity (the theory that describes black hotels), it is as close as one can orbit without constantly firing thrusters to keep from failing in. I had no confidence that my piloting skills could keep me out of trouble if I went closer. The corona at this distance exhibited less orderly motion than I was later to find in the disk of Cygnus X-1. Gas was rushing around in all directions. In some sectors it was plunging inward; in others it seemed to be blasting outward in a comparably chaotic rush. Superimposed on these turbulent eddies,
the gas was swirling around the hole faster and faster the closer I got. The pressure was so high that I expected it to enhance the effect of gravity in sweeping gas into the hole at a prodigious rate, by pushing inward as gravity pulled. Yet just the opposite seemed to be happening. As the gas was pressed toward the hole, it only swirled faster, and that just seemed to make it stiffen, somewhat like hard rubber. The stiffness of the gas seemed to be holding it back, enabling it to resist the black hole’s lure even as it crossed the 24-million-kilometer threshold from which I watched. Where did it begin its final plunge? I peered toward the hole and barely made out, at about 16 million kilometers from the hole, what looked like a sudden drop in the glow from the gas. I convinced myself that this was where the pressurized resistance to gravity failed and the gas thinned out as it was finally sucked in. But let me be honest: The appearance was so subtle and nondescript that to this day I do not know whether I saw the Milky Way’s giant black hole swallow anything of substance.
    There is an old saying among astronomers that