A black hole isn't "black," in the sense that a dinner jacket or the ink on a piece of paper is black. A black hole is a lot blacker than that. No human being has ever seen real blackness, because blackness is the absence of all light. It can't be seen. There is nothing to see. The blackest dye reflects a little light; a black hole reflects nothing at all. If you tried to illuminate it with the brightest searchlight in the universe-if you concentrated all the light of a quasar on it in a single beam-you would still see nothing. The tremendous gravitational force of the black hole would suck all that light in and it would never come out again. It can't.
It is a matter of escape velocity. The escape velocity from the Earth is seven miles a second; from a neutron star as much as 120,000 miles per second. But the escape velocity from a black hole is greater than the speed of light. The light doesn't "fall back" (as a rock thrown up from Earth at less than escape velocity will fall back to the ground). What happens to the light rays is that they are bent by the gravitational pull. The radiation simply circles the black hole, spiraling endlessly, never getting free.
And when a black hole passes in front of, say, a globular cluster,
it doesn't hide the cluster. It simply bends the cluster's light around
it.
If Victory's crew had wasted seven days, they still had five days' worth of supplies left before they had to start back to Gateway. They used them all. They took readings on the black hole even when they couldn't see it ... and when at last they got back to Gateway they found that one, just one, of their pictures had paid off.
They shared a five-hundred-thousand-dollar bonus simply for the pictures of the globular cluster. But the one picture that they hadn't even noticed when they took it-a split-second frame, taken automatically when no one happened to be watching the screen-showed what happened when the black hole occluded a bright B-4 star, a few hundred light-years away. That star hadn't moved up or down. By chance it had passed almost exactly behind the black hole. Its light had spread to surround the hole, like a halo; and that gave them a measure of the hole's size .
And then, long after they were back in Gateway, the research teams that studied their results awarded them another half a million, and the information that they were very lucky.
Marianna Morse had wondered about that: Why had the Heechee used an armored Five to visit this harmless object? Answer: It hadn't always been harmless.
Most black holes are not safe to visit. They pull in gases in accretion rings, and the acceleration of the gases as they fall produces a hell of radiation. Once this one had, but that was a long time ago. Now it had eaten all the gases in its neighborhood. There was nothing left to fall and so generate the synchrotron flux of energy that might fry even an armored Five if it lingered too long nearby .
and so the crew of Victory, without knowing it at the time, had had an unexpected stroke of luck. They arrived at the neighborhood of their black hole after its lethal feeding frenzy had ended, and so they had come back alive.
In its first twenty years the Gateway Corporation handed out more than two hundred astronomical science bonuses, for a total of nearly one billion dollars. It paid off on double stars and supernova shells; it paid off on at least the first examples of every type of star there was.
There are nine members of the catalogue of star types, and they are easily remembered by the mnemonic "Pretty Woman, Oh, Be A Fine Girl, Kiss Me," which runs the gamut from youngest to longest-living stars. The stellar classes from A down to the dim, small, cool Ms didn't earn any special science bonuses unless there was something truly remarkable about them, because they were too common. The vast majority of stars were dim, small, and cool. Contrariwise, the Os and Bs were hot young stars, and they always got bonuses because they were so few. But the Gateway Corporation awarded double bonuses on the P and W classes: P for gas clouds just condensing into stars, W for the hot, frightening Wolf-Rayet type. These were new stars, often immense ones, that could not be approached safely within billions of miles.
All those lucky prospectors collected science bonuses. So did the ones who happened to find themselves near known objects, at
