“In other words, you have an ordinary star and a black hole orbiting each other as a stable system,” Borel interjected.
“That is so. However, the system is not quite permanently stable. You see, the gravitational attraction of the black hole is strong enough for it to draw off gaseous material from the surface of the star. The system thus comprises three parts essentially: the visible star, the black hole, and a filament of stellar material that flows out of the former into the latter, connecting them rather like an umbilical cord. The filament spirals around the black hole as the particles contained in it acquire energy and accelerate down the gravitational gradient. In a somewhat simplified way, you might picture it as bathwater spiraling down into the drain.” He paused, allowing Borel to pose the next question.
“But straightforward as this might sound, it is producing results that you are having difficulty in explaining. Isn’t that so?”
“Very true,” Zimmermann agreed. “You see, the matter that is being drawn off of the visible star is extremely hot and therefore in a highly ionized state. In other words, it is made up of strongly charged particles. Now, charged particles in motion give rise to electromagnetic radiation; calculations predict that a characteristic spectrum of broad-band radiation, extending up into the x-ray frequencies, should be observable as a halo around the black hole. Indeed, we do observe radiation of the general nature that we would expect. Precise analysis of the spectrum and energy distributions, however, reveals a pattern that is not at all in accordance with theory.”
Zimmermann moved to one side and gestured toward the instrumentation panels behind them. “The equipment that you see here is being used for this kind of investigation. From here we can monitor and control the receiving equipment, direct the computers, and observe what they are doing.
“Many years of observations and measurements have enabled us to determine the characteristics of several black-hole binaries with sufficient accuracy for us to compute precisely a mathematical model that should give us the pattern of radiation that each should produce.” He moved forward to indicate one of the monitor screens on the console. “In fact, this is a picture of the theoretical distribution pattern computed for Cygnus X-l.” The screen showed a wavy green line, annotated with captions and symbols; it rose and fell in a series of peaks, valleys, and plateaus, like a cross-sectional view of a mountain range.
“This is what we should expect to see. But when we analyze the data actually received from Cygnus X1 . . .” he touched a button to conjure up a second, red curve, “we see that there is a significant discrepancy.” The screen confirmed his words. The red curve was of a different shape and lay displaced above the green curve; only in one or two places did the green rise high enough for the two to nearly touch.
“Both curves are to the same scale and plotted from the same origin,” Zimmermann commented. “If our model were correct, they would be approximately the same. It means that the amount of radiation actually measured is much greater than that which can be accounted for by theory.”
“Actual measurement shows more radiation than predicted,” Borel repeated. “Where does the excess radiation come from?”
“That, of course, is what intrigues us,” Zimmermann replied. “You see, there are only three objects in the vicinity—the star, the filament, and the black hole. We are quite confident that we know enough about the physics of ordinary matter—as exemplified by the star and the filament—to exclude them as possible sources. That leaves only the black hole itself. But how can a black hole produce radiation? That is the problem confronting us. You see, all our theories of physics, based on general relativity, tell us that nothing—matter, energy, radiation, information, or any kind of influence—can escape from a black hole. So how can the black hole be responsible for the extra energy that we detect as radiation? But there is nothing else there for it to come from.
“The answer to this question could have very far-reaching consequences.” The camera pulled in for a close-up. “Let us ask the question: What happens to matter when it falls into a black hole? We know that it disappears completely from the universe of which we have any knowledge. Logically, one must conclude that it exists thereafter either in some other part of our own universe or in some entirely different universe. There would appear to be no other possibility. If you reflect for a moment on the implications of what I have just said, you will realize why it is that we get excited at the discovery of what could turn out to be a process operating in the reverse direction. Something that contemporary theory declares impossible is being observed to happen. Behind it, we see hints of a whole new realm of physical phenomena and laws, of which we must at present admit an almost total ignorance. And yet we have strong reasons to suspect that within this mysterious realm, things that we consider to be impossible could turn out to be commonplace.”