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Black Holes

 

Another result that has come out of research in the science of gravity has been the prediction and then the discovery of that bizarre enigma, the black hole. It is truly a hole, in that anything dropped into it falls forever. It is truly black, in that nothing comes back out, not even light. Even the identity of what went into the black hole is obliterated by the blackness. The power of the black hole is so awesome that it even swallows space and warps time.

Black holes are forms of matter which are predicted not only by the Einstein Theory of Gravity, but many other theories of gravity. We now have good astronomical evidence that they really exist out in space. In our Milky Way galaxy there are probably millions of black holes containing the mass of a large star, while at the very center of our galaxy there is probably a huge black hole containing the mass of a million stars.

We don't have to worry about falling into these monsters of space-time, however, for they can only pull on us at long range with their gravity field, and they are so far away, their gravity field is many times weaker than the gravity field of the Sun. So, we will stay tied to the Sun, keeping comfortably warm, while the Sun orbits around the black hole at the center of the galaxy. After a nearly uncountable number of years, the orbit of the Sun will decay and the Sun will finally join the big black hole at the galactic core, but that will take place long after the Sun and all the rest of the stars in the galaxy have burned out. We and our robots will have left this worn-out galaxy long before that time and continued life in a new, fresh galaxy which we will have designed to suit our tastes.

The reason that a black hole is black, is that the gravity field of the black hole is so large that the escape velocity of the black hole is greater than the speed of light. The escape velocity of an ordinary massive object, like a planet, is the initial velocity a rocket must have in order to leave the surface of the planet and coast off into space without need for additional propulsion. For the Earth the escape velocity is 11 kilometers per second, at the surface of Jupiter it is 61 kilometers per second, and for the Sun it is 620 kilometers per second (0.2% of the speed of light). As long ago as 1795, it was noticed by the astronomer and mathematician, Pierre Simon, the Marquis de Laplace, that at the surface of a planet with the density of Earth and a radius some 250 times that of the Sun, the escape velocity would be equal to the speed of the corpuscles that light was thought to be made out of at that time. Laplace thus concluded that such a planet would be dark. This was the first speculation on the concept of a black hole.

Black holes became more than a speculation in 1915 when Albert Einstein formulated the equations for his Theory of Gravity, the General Theory of Relativity. Only months later, Karl Schwarzschild found one of the first solutions to those equations. Called the Schwarzschild solution, it describes the motion of a small test particle near a non-rotating massive sphere. The Schwarzschild solution is the relativistic replacement for the Newtonian equations that describe the orbits of the planets about the massive Sun.

The Schwarzschild solution to the Einstein Theory of Gravity gives the same results as the Newton Theory of Gravity for a test particle near a mass when the test particle and mass are far apart. But when the gravitating mass is very dense, so that the test particle can get very close, there are differences between the predictions of the Newton Theory of Gravity and the Einstein Theory of Gravity. One of these differences causes an extra precession in the orbit of the planet Mercury. Another causes light passing by the Sun to be bent inward. Another difference causes light signals passing by the Sun to take longer to travel because time runs slower near the Sun. This has been checked by tracking time signals from spacecraft as they pass in back of the Sun. Another difference is that photons of light "get tired" as they try to climb up a gravitational field. Unlike a stone, which slows its speed as its energy becomes less, photons, which must travel at the speed of light, are gravitationally redshifted to a lower frequency. The lower the frequency of a photon, the lower the energy. This gravitational red-shift effect has been measured by sending gamma-ray photons up a tower at Harvard and measuring their decrease in frequency as they climbed up out of Earth gravity.

Because we have measured all these effects, we know that the Schwarzschild solution to the Einstein Theory of Gravity is the best description of the gravity field outside a large mass. That solution, however, predicts some bizarre behavior when the mass is very large or very dense so the test particle can get close to it. One of those bizarre predictions is the black hole.

You will all be relieved to know that our Sun is a little too small to turn into a black hole all by itself. When it uses up all its energy it will turn into a white dwarf star. All of its mass will collapse into an object about half the size of the Earth, with a density that is a million times larger than that of normal matter. It will sit there glowing whitely from the heat of its collapse, slowly turn redder, and then turn dark as it cools off over billions of years. If our Sun had been two or three times more massive, the final collapse would not stop at the white dwarf star stage, but would proceed to the neutron star stage, where the mass of a star is compressed into a sphere some twenty kilometers across with a density of a hundred trillion times that of normal matter. If our Sun were larger than three solar masses, however, then the neutron star stage would not be stable.

In 1939, J. Robert Oppenheimer and his student showed that the nuclei in a collapsing star are not strong enough to resist the gravitational crushing forces if the initial mass of the star were large enough. Their paper was little noticed because of other things going on in the world in 1939. Oppenheimer became involved in those other things and it was not until after World War II that scientists came back to look at black holes. They found that there was no way to avoid the conclusion that the end point of the evolution of a star with a mass greater than three solar masses has to be a black hole.

A star turns into a black hole when the escape velocity of the star equals that of light. For a star with a given mass M this occurs when all the mass is concentrated inside a radius R called the "Schwarzschild radius" (R=2GM/c2). For typical stellar mass black holes, this radius is ten kilometers or so. When the collapsing star becomes this small, the star disappears from view and its place is taken by the "event horizon". The event horizon is a highly warped region of spacetime that separates the outside universe from the miniature universe inside. It is a one way membrane, in that objects can fall in through the event horizon, but things inside the event horizon cannot get back out. It is also the infinite red shift boundary, since light emitted from an object at that radius is infinitely gravitationally redshifted to zero energy. It is the event horizon that is the black hole, not the star. After the event horizon is formed by a collapsing star, the collapse of the star continues on in the same manner as it did before the event horizon formed. The star gets denser and smaller in radius as it collapses. The event horizon, however, stays constant in size after it has formed, with a radius equal to the Schwarzschild radius. In essence, the event horizon is a black shield that prevents anyone from seeing what is going on inside. (It is interesting to note that "Schwarzschild" means "black shield" in German.)

Theoretically, black holes can come in many different sizes and densities. The typical black hole that one reads about in the Sunday supplements is the very dense black hole that is a few tens of kilometers across and has the mass of a number of suns. It is a large star collapsed into a volume the size of a large mountain. The density is 1018 times that of normal matter and even 1,000 times that of nuclear matter. A stellar mass black hole is probably spinning fairly rapidly since the original star from which it was formed was likely to be rotating somewhat. During the collapse of the star to form the black hole, the angular momentum in the original star was conserved, leaving the black hole spinning rapidly. The collapsing star increases its spin speed for the same reason that an ice skater increases her spin speed when she pulls in her outstretched arms during a toe spin.

The solution to the Einstein gravity equations that describes a rotating black hole was found by the mathematician Roy Kerr in 1963, almost fifty years after the solution for the nonrotating black hole. The Kerr solution reduces to the Schwarzschild solution when the rotation of the black hole is zero. Recently, other mathematicians have shown that these two solutions describe the only stable configurations for an uncharged black hole.

The black hole could have lost more electrons than protons during the collapse process, so it could have a modest electric surface charge, and since the black hole is spinning, that rotating electricity would produce a magnetic field. The solution for a charged, rotating black hole ring was found by Newman in 1965 as a solution to the combined Einstein gravity equations and Maxwell electromagnetic equations.

One important characteristic about a black hole is that after it is formed, the only things you can measure about the final configuration are its mass, angular momentum, charge, and magnetic field—nothing else. A black hole made out of a collapsing star looks exactly like a black hole made out of a collapsing antimatter star, or for that matter, a black hole made out of a few solar masses of televisions, moldy cheese, or anything.

One convincing candidate for a black hole is the X-ray source Cygnus X-1. Because it is a source of rapidly varying X-rays it must be a compact star, either a white dwarf, neutron star, or black hole. The X-ray source is in orbit around a companion star that is a typical blue supergiant with a mass of about twenty solar masses. The orbital period of 5.5 days obtained from the X-ray data then gives us an estimate for the mass of the X-ray source of eight solar masses. Since stellar theory puts an upper limit on the mass of a neutron star of three solar masses, and this source is well beyond that limit, it must be a black hole.

What does a black hole look like? As a star turns into a black hole, the time it takes for it to turn black is very rapid. In a few milliseconds it goes from full luminosity to less than a billionth of full luminosity. For a human observer, a collapsing star essentially disappears instantaneously. An observer near a collapsing black hole can be one of two kinds, a static observer who sits at rest in the external field of the black hole supported by a powerful rocket, or a free-fall observer who falls into the black hole along with the stellar matter.

When either observer is far from the black hole and looks in the direction of the black hole he sees a black disk. Around that black circle he can see the normal star pattern, except near the black hole the star pattern is distorted. The black hole does not cover up the star pattern as it passes in front of it, instead the black hole disk seems to "expel" the points of light from that region of the sky. A star image moves to one side or the other of the black disk and slides up and over. If the star image and the center of the black hole disk exactly coincide, then the star image momentarily breaks up into a bright ring of light around the black disk where the photons from the star in back of the black hole have been bent by gravitational focusing. (There are actually a number of rings, one where the photons circled the black hole once before they flew off toward the observer, one inside that where the photons circled twice before they flew off, etc.)

As the static observer moves closer and closer to the horizon the black hole disk gets larger and larger and completely fills the sky. Then all the infalling radiation from the rest of the Universe is observed as a very tiny, highly blue-shifted, incredibly bright spot in the "up" direction. The reason the light is so bright is that the static observer is "accelerating" toward the light in his rocket ship instead of free-falling along with the light.

For a free-fall observer, the view toward the black hole is also black, and it grows in size as the observer falls toward the black hole. But unlike the static observer, the dark patch in the forward direction of the sky never extends around into the back hemisphere. Half of the free-fall observer's sky (or more in the early stages far from the black hole) is always filled with the external star pattern. Because the Doppler red shift of the free-fall observer moving away from the distant stars more than compensates for the gravitational blue shift, the photons from the distant stars are red shifted everywhere, except in a bright band near the observer's equator where they are blue shifted. The free-fall observer notices nothing unusual when he falls through the event horizon. All the observing stops, of course, when the observer hits the singularity at the center of the black hole.

Not all black holes have high density. The larger a black hole, the smaller the density. We are probably living inside a black hole—the Universe. The Universe is very massive, so it doesn't have to be very dense to form a black hole. In fact, if you calculate the density of a black hole the size of the Universe, you find that the density required is one atom per cubic centimeter, very close to the average density of space in our galaxy. Present estimates by astronomers of the average density of the visible mass in the Universe, however, leave us a factor of ten short. This has led to a search for the so-called "missing matter" that is needed to bind up the Universe into a nice neat package. Many candidates for the missing matter, such as massive neutrinos, brown dwarfs, miniature and supermassive black holes, and massive "axion" particles have been proposed, but whether the Universe is closed or open is still an open question. If the Universe is closed and is therefore a black hole, then one could ask why it isn't collapsing. It is, or at least it is trying to, but for some unknown reason the Universe got started with a big bang that has all the matter flying outward. After a long enough time, the gravitational pull will overcome the initial momentum and the Universe will collapse.

One could have a black hole that is galactic in size. The average galaxy has about 100 billion stars. If you crammed all those stars into a volume with a radius of about 2000 times that of the distance between the Earth and the Sun (an astronomical unit or AU), you would form a black hole. Although this black hole is only about eleven lightdays in radius, the spacing between the stars would still be large enough, almost one AU, that collisions between the stars would be infrequent. If our solar system fell into such a galactic-sized black hole, the tides from the miniuniverse would be strong enough to separate the planets from the Sun, but they would not be strong enough to do damage to the planets or the Sun itself. The difference in gravity across the diameter of the Earth as the Earth approached the "event horizon" of this incipient black hole universe would be insignificant, about forty microgravities. You wouldn't feel a thing as the Earth fell into a black hole of this size. From the viewpoint of an observer inside the miniuniverse, the Earth would pop into view out of nowhere into the middle of space.

What would it be like to live in a miniature closed universe like this? You will only have a few days to look around, since this miniuniverse is eleven lightdays in radius and is collapsing at nearly the speed of light, but let us imagine that you have at your disposal a rocket ship with a faster-than-light warp drive. You take off from Earth in your rocket ship on a journey into the unknown like a future Magellan to explore this compact universe only 4000 AU in diameter. You would leave going in a straight line away from Earth, always keeping it in sight through a telescope pointed directly behind. After you had traveled about one-third the way across/around your universe, the view through the rear telescope would show a greatly magnified view of Earth because the strong gravity of all the stars between you and the planet would curve the light rays, giving a magnified image. At the half-way point in your journey, the image of Earth through the rear telescope would have expanded to fill practically the whole rear hemisphere of view. At the same time, a lookout peering through a front telescope would see the same magnified view of Earth, but of its other side. As you completed your journey, the view of Earth through the rear telescope would continue to expand and become fainter, while the view through the forward telescope would shrink until it coincided with the view of the real thing through the forward porthole as you return triumphantly back home, having circumnavigated the Universe while always traveling in a straight line.

It is as difficult for us to imagine living in a closed, finite, curved universe as it was for early man to comprehend living on a closed, finite, curved world. Since there were only six continents and seven seas on the Earth, it seemed obvious at the time that when you come to the last continent there had to be an edge to the world somewhere. But we now know that there is no edge anywhere on the globe. It is the same in our galactic-sized miniuniverse. Even through there are a lot of stars, there are a finite number. As you go to each one and look around, each star seems to be at the "center" of the universe, with equal numbers of stars in all directions. There is no edge, there is no way out, and alas, the singularity approaches.

Although large black holes have interesting properties and characteristics and are fun to speculate about, it will be a long time, if ever, before we could attempt to make them in order to develop some form of future technology. But black holes can come in many sizes, and the smaller ones involve masses that are small enough for the human race to dream about using in new technologies that are presently indistinguishable from magic.

Small black holes were first discussed in the scientific literature by Stephen Hawking. It had long been known that for a black hole to form spontaneously by gravitational collapse, the amount of mass involved had to be larger than the mass of the Sun. Hawking speculated that miniature black holes much smaller than the Sun could have been formed by the Big Bang at the beginning of the Universe when the pressure of light and other matter was very high. They could be any size, from solar masses down to about ten micrograms.

These small black holes are very dense and very interesting. They have very small diameters, most of them much smaller than an atom, with the smallest, the ten microgram mass version, being only 10-35 meters across. The miniature black holes would be attracted by the Earth, the other planets, and by the Sun into orbital trajectories. Most of these orbits would be elliptical orbits out in space around the Sun. Since the miniature black holes are so tiny and so dense, however, they could even be in an orbit that passed right through the Sun or a planetoid.

Although they are small in size, the miniature black holes would have a significant gravity field. In passing through a body made of normal matter, a miniature black hole would produce powerful tidal forces at atomic ranges that would cause drag to take place. After bouncing back and forth through a planetoid a number of times, the miniature black holes would slow down and be captured. There could be swarms of them in the center of the Sun and planets, slowly eating them up. The rate of capture is very low, however, since the miniature black holes are so small they can only swallow one atom at a time.

A few years after Stephen Hawking invented the concept of miniature black holes, he found a way to make them disappear! While going through some detailed calculations about the interaction of the ultrastrong gravity field of these ultradense objects on the space-time vacuum near their surface, he discovered that his newly invented miniature black holes would not be black. They would seem to glow instead.

Stephen Hawking has developed a picture one can use to attempt to understand the reason why black holes look like they are emitting radiation. According to the theory of quantum mechanics, what we call vacuum is not empty, but is full of pairs of "virtual particles" that are created temporarily out of nothing, exist for a while, then merge back into nothing. [See top half of Figure 11.]

Most of the virtual particles in the vacuum are low energy photons, but even charged particle pairs like electrons and positrons occasionally appear for a short period of time. If a small black hole were placed in this emptiness full of energy, its powerful gravitational field would swallow one of the virtual particles if it got too close. [See bottom half of Figure 11.] With no partner to recombine with, the other member of the virtual particle pair would be promoted to the status of a "real" particle and leave. To an onlooker, it would look as if the black hole "emitted" the particle.

In this model of the interaction of a miniature black hole with the vacuum, the black hole emits radiation and particles, as though it had a temperature. The temperature would be inversely proportional to the mass of the black hole. A Sun-sized black hole is very cold, with a temperature of about a millionth of a degree above absolute zero. When the mass of the black hole is about a hundred billion tons (the mass of a large asteroid), the temperature is about a billion degrees.

 

067187686411.jpg
Fig. 11 - "Empty" space filled with virtual particles,
with and without a quantum black hole.

 

According to Donald Page, who carried out lengthy calculations on the subject, such a hole should emit radiation that consists of approximately 81% neutrinos, 17% photons, and 2% gravitons. When the mass becomes significantly less than a hundred billion tons, the temperature increases until the black hole is hot enough to emit electrons and positrons as well as radiation. When the mass becomes less than a billion tons (a one kilometer diameter asteroid), the temperature now approaches a trillion degrees and heavier particle pairs, like protons and neutrons are emitted. The size of a black hole with a mass of a billion tons is a little smaller than the nucleus of an atom. The black hole is now emitting 6000 megawatts of energy, the output of a large power plant. It is losing mass at such a prodigious rate that its lifetime is very short and it essentially "explodes" in a final burst of radiation and particles.

Thus, those black holes that have a mass significantly greater than a billion tons have a low temperature, are losing mass slowly, and have a lifetime longer than the present fifteen billion year age of the Universe, so they would still be around if they were formed during the Big Bang. Those miniature black holes that are significantly less massive than a billion tons would have evaporated long since.

No one has found any evidence of tiny black holes. If there are any trapped in the Earth or Sun, it would be difficult to prove it. There is, however, one indication that there might be some miniature black holes in the center of the Sun. Most of the fusion reaction burning that takes place in the Sun occurs in a small dense hot region near the center. According to theory, the fusion reactions go through a complicated cycle that converts hydrogen atoms into helium, then burns the helium to produce carbon, oxygen, nitrogen, and the other elements up to iron. The theoretical calculations, backed by atom-atom collision experiments on Earth, are now able to predict the present size, temperature, and burning rate of the Sun quite accurately. They also predict that the fusion reactions at the center of the Sun should produce a large flux of neutrinos. The neutrinos, being able to pass through lightyears of lead without being stopped, immediately leave the center of the Sun, while the heat and light generated in the core of the Sun takes ten million years to get out through the optically opaque outer layers of the Sun.

There are so many neutrinos coming from the Sun that it is possible to detect them on Earth despite their low interaction rate. A number of different detectors for solar neutrinos have been operating for many years now, but the number of detected neutrinos has been one-third that predicted by the otherwise successful solar fusion theory.

One explanation for the low numbers of observed neutrinos is that there are miniature black holes in the center of the Sun helping along the fusion process. That means the normal fusion process doesn't need to be as active and as a result emits fewer neutrinos. There are other explanations for the shortage of solar neutrinos, but most of them are just as speculative as the miniature black hole explanation.

If it turns out that small black holes really do exist, then I propose that we go out to the asteroid belt and mine the asteroids for the black holes that may be trapped in them. If a small black hole was in orbit around the Sun in the asteroid belt region, and it had the mass of an asteroid, it would be about the diameter of an atom. Despite its small size, the gravity field of the miniature black hole would be just as strong as the gravity field of an asteroid and if the miniature black hole came near another asteroid, the two would attract each other. Instead of colliding and fragmenting as asteroids do, however, the miniature black hole would just penetrate the surface of the regular asteroid and pass through to the other side. In the process of passing through, the miniature black hole would absorb a number of rock atoms, increasing its weight and slowing down slightly. An even more drastic slowing mechanism would be the tides from the miniature black hole. They would cause stresses in the rock around the line of penetration and fragment the rock out to a few micrometers away from its path through the asteroid. This would cause further slowing.

After bouncing back and forth through the normal matter asteroid many times, the miniature black hole would finally come to rest at the center of the asteroid. Now that it is not moving so rapidly past them, the miniature black hole could take time to absorb one atom after another into its atom-sized body until it had dug itself a tiny cavity at the center of the asteroid. With no more food available, it would stop eating, and sit there and glow warmly for a few million years. After years of glowing its substance away, it would get smaller. As it got smaller it would get hotter since the temperature rises as the mass decreases. Finally, the miniature black hole would get hot enough to melt the rock around it. Drops of melted rock would be pulled into the miniature black hole, adding to its mass. As the mass of the black hole increased, the temperature would decrease. The black hole would stop radiating, the melted rock inside the cavity would solidify, and the process would repeat itself many centuries later. Thus, although a miniature black hole left to itself has a lifetime that is less than the time since the Big Bang, there could be miniature black holes with the mass of an asteroid, being kept alive in the asteroid belt by a symbiotic interaction with an asteroid made of normal matter.

To find those asteroids that contain miniature black holes, you want to look for asteroids that have anomalously high temperatures, lots of recent fracture zones, and anomalously high density. Those with a suspiciously high average density have something very dense inside. To obtain a measure of the density, you need to measure the volume and the mass. It is easy enough to get an estimate of the volume of the host asteroid with three pictures taken from three different directions. It is difficult to measure the mass of an object in free fall. One way is to go up to it with a calibrated rocket engine and push it. Another is to land on it with a sensitive gravity meter. There is, however, a way to measure the mass of an object at a distance without going through the hazard of a rendezvous. To do this, you need to use a mass detector or gravity gradiometer. This is a device that measures the gradient or the changes in the gravity attraction with distance. These gravity gradient forces are the tidal forces by which the Moon causes tides to rise on the Earth, even though both the Earth and the Moon are in free fall. There are a number of different ways to make a gravity gradiometer. The one that I invented uses two dumbbell shaped masses connected together at the center in the shape of an X. [See Figure 12].

When a single dumbbell is placed near a gravitating body such as an asteroid, one mass or the other on the dumbbell will be closer to the asteroid. Since the gravity field of the asteroid gets stronger with decreasing distance, the near mass of the dumbbell will be pulled harder than the far mass, causing the dumbbell to ultimately align itself with the direction to the asteroid. This natural alignment of a long object in orbit around a gravitating body is used by many Earth-pointing satellites and by the Space Shuttle during resting periods. By building my gradiometer with two crossed dumbbells at right angles to each other, one dumbbell is torqued clockwise while the other is torqued counterclockwise. The amount of differential torque between the two arms is measured by determining the change in angle between the two arms. This is a lot easier than trying to measure the angle of one arm with respect to some reference direction.

 

067187686412.jpg
Fig. 12 - Method of operation of the Forward Mass Sensor.

 

I use one more trick in the operation of the gravity gradiometer instrument that I invented. I deliberately rotate the sensor at fifteen revolutions per second. In this rotating reference frame, the tiny differential angles between the two arms turn into tiny differential vibrations, and it is a lot easier to measure vibrations than angles. My gravity gradiometer could detect the mass of my fist at thirty centimeters (one foot), me at two meters (I mass over 100 kilograms), and an asteroid-sized black hole at 1000 kilometers.

Once you have found a suspiciously warm asteroid that seems awfully massive for its size, then to extract the miniature black hole, you give the surface of the asteroid a strong shove and push the asteroid out of the way. The asteroid will shift to a different orbit, and where the center of the asteroid used to be, you will find the miniature black hole. The black hole will be too small to see, but if you put an acoustic detector on the asteroid you will hear the asteroid complaining as the black hole comes to the surface. Once the black hole has left the surface you can monitor its position and determine its mass with a mass detector.

It is not too dangerous being near a black hole if you are careful. A modest sized one, with a mass equivalent to that of a 250 meter diameter asteroid made of rock, would have a gravity field of about one Earth gravity at a distance of thirty centimeters (a foot). If you approached this miniature black hole by yourself, you would be in danger unless you carefully put yourself in orbit about it ten meters or more away (your orbital period at ten meters distance would be about four minutes). Two people could get right up next to the miniature black hole if they put their hands and knees together to make a space between them. Their combined center of mass is now in the space between them, and if they carefully arrange their approach so that the trajectory of the black hole does not intersect either of them, they can put the black hole between them where they can both take a close look. The gravity forces they would experience would be about the same as if they were crawling on their hands and knees on a floor back on Earth. A black hole the size of an asteroid is smaller than an atom, so you can't see it directly. It will cause bending of light rays passing by it, however, so you could see it by placing a fine illuminated grid in back of it and looking through a microscope at the grid to find a flaw. The flaw will be caused by the bending of the light by the black hole floating in front of the grid.

The next step in corralling the invisible black maverick is to put some electric charge on it. This means bombarding the position of the miniature black hole with a focused beam of ionized particles until the black hole has captured enough of them to have a significant charge to mass ratio. The upper limit will depend upon the energy of the ions. After the first ion is absorbed, the black hole will have a charge and will have a tendency to repel the next ion. Another upper limit to the amount of charge you can place on a black hole is the rate at which the charged black hole pulls opposite charges out of the surrounding space. You can keep these losses low, however, by surrounding the black hole with a metal shield.

Once a black hole is charged, you can apply forces to it with electric fields. If the charged black hole happens to be rotating, you are in luck, for then it will also have a magnetic field and you can also use magnetic fields to apply forces and torques. The coupling of the electric charge to the black hole is very strong—the black hole will not let go. You can now use strong electric or magnetic fields to pull on the black hole and take it anywhere you want to go.

If the black hole were very small, only boulder sized, and you were successful in getting and keeping a lot of charge on it, you could conceivably bring the charged miniature black hole down to Earth and keep it there. The force that can be applied to a maximally charged black hole by a reasonably strong electric field of a few hundred thousand volts is more than enough to levitate a boulder-sized black hole in the gravity field of the Earth. The chances of losing the black hole due to a power failure or other accident would be high enough, however, that it would be better if black holes were left in high orbit.

Once you have charged black holes that you can manipulate at will, then you can use them in a number of ways. By putting them in a mixture of deuterium and tritium gas, you can cause fusion reactions to take place without having to have the deuterium-tritium mixture at high temperatures and pressures. The black hole will act as a catalyst for the fusion reaction. The density of the deuterium-tritium gas near the black hole will be greatly increased by the gravity forces of the black hole and the fusion rate in that region will increase dramatically, creating a "hot spot". Most of the reaction products will come out of that region and deposit their energy in the rest of the gas and the usual shielding around the fusion reaction chamber. The resultant heat can then be used to power a thermal power plant. A few deuterium and tritium atoms will be lost to the black hole, but those losses should be small.

Even if miniature black holes are never found and the only black holes we ever have are large stellar and galactic sized collapsed masses, these large black holes may still be very valuable in directing us toward some still unknown form of future technology that is indistinguishable from magic. For by merely observing these objects in detail as they interact with the matter around them, we will be observing phenomena that we cannot replicate on Earth, or even in our solar system. Phenomena involving warped space, distorted time, and contorted ultradense matter that will test our theories as we stretch them to cover these bizarre happenings. We are learning, and will continue to learn, as we attempt to model what we see, and out of that learning will come new, better, theories that are the spells that we will need to invoke new forms of future technology that are presently indistinguishable from magic.

Then, if we can find (or make, by using our new theories) miniature black holes, we will have the magic wand that we will need to bring new forms of future magic into being. Limitless sources of energy, gravitational communication, space warps, time machines, and more, might be ours. Some of these new technologies we may see in the near future, some we may see in the far future, some may never be in any future—all would be indistinguishable from magic to us today.

 

Recommended Reading

Stephen Hawking, "Gravitationally Collapsed Objects of Very Low Mass," Monthly Notices Royal Astronomical Society, Vol. 152, pp. 75 ff (1971).
 

Stephen Hawking, "The Quantum Mechanics of Black Holes," Scientific American, Vol. 236, #1, pp. 34 ff (January 1977).
 

J.B. Hutchings, "Observational Evidence for Black Holes," American Scientist, Vol. 73, pp. 52 ff (1985).
 

William J. Kaufmann, III, The Cosmic Frontiers of General Relativity, p. 110 (Little, Brown and Co., Boston, 1977).
 

Kip Thorne, "The Search for Black Holes," Scientific American, Vol. 231, #6, pp. 32 ff (December 1974).

 

 

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