Cosmic Connection
Page 23
The first black hole may have been found. Cygnus X-1 is a rapidly varying source of X-rays, visible light, and radio waves. Its X-ray emission was monitored from NASA’s UHURU satellite, launched from an Italian launch complex off the coast of Kenya. All the clues point to Cyg X-1’s being a binary star, two stars revolving around each other in a regular and intricate waltz. From the motion of the one star we see, we can deduce the mass of the star we cannot. It turns out to be a massive star, perhaps ten times the mass of our Sun. Such a massive star should ordinarily be very bright. Yet there is no optical hint of its presence. The bright star in Cyg X-1 is revolving about a massive object that is present gravitationally but not optically. It is very likely a black hole a few thousand lightyears from Earth.
Black holes may have their uses. What we know about them till now is entirely theoretical, not tested against the skeptical standards of observation. There are some strange possibilities that have been suggested for black holes. Since there is no way to get out of a black hole, it is, in a sense, a separate universe.
In fact, our own universe is very likely itself a vast black hole. We have no knowledge of what lies outside our universe. This is true by definition, but also because of the properties of black holes. Objects that reside in them cannot ordinarily leave them. In a strange sense, our universe may be filled with objects that are not here. They are not separate universes. They do not have the mass of our universe. But in their separateness and their isolation they are autonomous universes.
There is an even more bizarre prospect. In one speculative view (Chapter 36), an object that plunges down a rotating black hole may re-emerge elsewhere and elsewhen–in another place and another time. Black holes may be apertures to distant galaxies and to remote epochs. They may be shortcuts through space and time. If such holes in the fabric of the space-time continuum exist, it is by no means certain that it would ever be possible for an extended object like a spacecraft to use a black hole for travel through space or time. The most serious obstacle would be the tidal force exerted by the black hole during approach–a force that would tend to pull any extended matter to pieces. And yet it seems to me that a very advanced civilization might cope with the tidal stresses of a black hole.
How many black holes are there in the sky? No one knows at present, but an estimate of one black hole for every hundred stars seems modest by at least some theoretical estimates. I can imagine, although it is the sheerest speculation, a federation of societies in the Galaxy that have established a black hole rapidtransit system. A vehicle is rapidly routed through an interlaced network of black holes to the black hole nearest its destination.
At a typical place in the Galaxy, one hundred stars are encompassed within a volume of radius of about twenty light-years. If we imagine relativistic space vehicles for the short journeys–the local trains or shuttles–it would take only a few years’ ship time to get from the black hole to the farthest star of the hundred. One year on board the relativistic shuttle would be occupied accelerating at about 1 g, the acceleration we are familiar with because of the gravity of Earth. After one year at 1 g, we would approach the speed of light. Another year would be spent doing a similar deceleration at 1 g at the end-point of the journey. A galaxy with such a transportation system, a million separately arisen civilizations and large numbers of worlds with colonies, exploratory parties, and work teams–a galaxy where the individuality of the constituent cultures is preserved but a common galactic heritage established and maintained; a galaxy in which the long travel times make trivial contact difficult, and the black hole network makes important contact possible–that would be a galaxy of surpassing interest.
I can imagine, in such a galaxy, great civilizations growing up near the black holes, with the planets far from black holes designated as farm worlds, ecological preserves, vacations and resorts, specialty manufacturers, outposts for poets and musicians, and retreats for those who do not cherish big-city life. The discovery of such a galactic culture might happen at any moment–for example, by radio signals sent to the Earth from civilizations on planets of other stars. Or such a discovery might not occur for many centuries, until a lone small vehicle from Earth approaches a nearby black hole and there discovers the usual array of buoys to warn off improperly outfitted spacecraft, and encounters the local immigration officers, among whose duties it is to explain the transportation conventions to newly arrived yokels from emerging civilizations.
The deaths of massive stars may provide the means for transcending the present boundaries of space and time, making all of the universe accessible to life, and–in the last deep sense–unifying the cosmos.