Black Holes !

A black hole is the ultimate “dangerous object.” You get a regular hole by digging stuff out of it. The more you dig, the bigger the hole. Holes can be dangerous just because they are big. If you find yourself trapped in a hole, the first thing you should do is stop digging. There are holes, black holes, and the Black Hole of Calcutta. That was a dangerous hole, but not nearly as dangerous as a relativistic black hole. Some people actually got out of there alive, and it even had a couple of small windows. With a relativistic black hole, there’s no chance of either.

Let’s “Numinate” about these relativistic black holes—how they could come about, and what they would be like. First of all, you shovel stuff into them—you don’t get a black hole by digging stuff out of it. As you pile more and more stuff together, gravity becomes greater and greater. The gravity at the surface of an object depends on how much mass the object has and how dense it is. An object with a given amount of mass has a higher surface gravity the more its mass is concentrated into a smaller volume—in other words, as its density is increased.

Theory has it that black holes can come in any size. They could be microscopic or astronomic. They aren’t really measured by size so much as by the mass they contain. A black hole can result from any amount of mass—no matter how little— if it’s squeezed into a small enough volume. Any concentration of matter produces gravity. Large, hot concentrations are called stars. Our sun is a star. Smaller, cooler concentrations of matter are called planets if they circle a star, or moons if they circle a planet, or asteroids if they are small enough.

Each of these objects, due to the gravity at its surface, has a particular escape velocity. That is, if you were standing on its surface and threw a rock away from it fast enough, the rock would escape and never fall back. The escape velocity of the earth is 25,000 miles per hour. This means you would have to fire a bullet from the surface of the earth at about seven miles a second for it to escape into outer space. If you fine-tuned the speed just right, the bullet would orbit the earth once, come full circle, and hit you in your back. At any speed less than escape velocity, whatever goes up, comes back down.

Imagine objects with higher and higher surface gravities. They would have higher and higher escape velocities. When you talk about ever higher velocities, of course, you eventually reach a limit—the speed of light. A black hole is simply an object whose escape velocity is greater than the speed of light. If you were standing on the surface of an object whose escape velocity were exactly equal to the speed of light, a beam of light from your flashlight would orbit once around it and shine on your back. All light emitted from the object would fall back onto it. No light would escape. No light could bounce off the object either. The object would be absolutely black from a point of view some distance away. Thus, the name “black hole.”

Large black holes could come about in the natural life span of a star about three times the size of our sun. When this amount of matter accretes into a star, a series of nuclear fusion reactions is triggered. Each step in this series involves the fusion of heavier atoms into still heavier ones. The series stops when the atoms are too heavy to undergo another fusion cycle. We believe this point to be reached when the matter is largely iron. Now, what happens? Up to this point, the star is kept from gravitational collapse by the massive conversion of matter into energy. This energy, in the form of heat, holds the atoms apart. When no more energy is available, the star begins to cool. Now, the star literally collapses under its own weight. This is the story of the smallest of the large black holes. It involves the “death” of stars three or more times the mass of our sun.

Very large and very small black holes would come about in different ways—very different from one another—and very different from the “death of a star” scenario. This is because a small black hole relies on matter compressed to fantastic densities to get it into a small enough volume that its escape velocity exceeds the speed of light. Such densities might be a by-product of the “death” scenario, or perhaps of some bigger Bang scenario. As you increase the mass of a black hole, the critical volume goes up and the critical density goes down. When a very large mass is involved, the density doesn’t even have to be that great. Inside a very large black hole there could easily be normal stars and vast swirling vortices of dust and debris. Such a black hole would be very like a universe unto itself.

Our conception of a black hole is based on the model we call the general theory of relativity (again, we encounter Einstein). Various extrapolations have been made from the simple logic that says: light can’t escape from a region whose escape velocity exceeds that of the speed of light. And, since nothing can travel faster than light, nothing else can escape either. Two of the more common extrapolations about black holes are that escape from them is impossible, and that they contain a singularity inside them.

The fact is, these theories have never been tested. Other models are possible. It’s hard to believe in a model proposing that all matter in the universe erupted out of a single point in an event called the Big Bang, and one that also says matter can disappear forever into a black hole.

Let’s see if we can find a plausible way out of a black hole. When we launch a rocket into outer space it needn’t reach the escape velocity of seven miles a second. If a rocket has enough fuel, it can rise as slowly as you like and still escape the gravity of the earth. The point is that it doesn’t have to reach “escape velocity” to actually escape. It’s kind of like climbing out of the Grand Canyon: you might not go very fast, but at the end of the day you have escaped. A guy who’s still at the bottom can’t hit you with a .22 from his rifle, because the bullet doesn’t travel fast enough to reach the canyon rim. Escape is a tradeoff between speed and persistence.

Perhaps escape is possible, but how do we avoid the singularity inside? What is a singularity, anyway? Imagine crowding lots of atoms into a very small space. At first, their atomic structure holds them apart. The electrons around each atom repel those of the atom next to it. But you are relentless, you keep adding more and more atoms, increasing the force of gravity until the mutual repulsion of the electrons is overcome. Now, the nucleus of one atom and that of the next are forced ever closer together. You keep piling them on, increasing the force of gravity until even the repulsion between one nucleus and the next is overcome. At some point gravity exceeds all the forces that hold matter apart, and then? Theory has it that matter, at that point, is drawn together without limit. Everything caught in such a collapse disappears into a point called a singularity. This happens at densities well beyond the point at which matter vanishes into a black hole. This happens at densities so extreme that the standard model of what happens when you crush atoms might not extrapolate. Let’s look at a scenario that might allow escape from a black hole long before a singularity would occur.

The key to escaping a black hole would be a sustained outward force. For example, if matter reached a sufficient density, it might begin to annihilate itself. A fireball of energy would be produced that could sustain an outward pressure for a period of time. Time enough that the black hole’s strangle hold might be broken. This fireball would just have to be persistent, it wouldn’t have to produce escape velocity.

How would such an annihilation occur? The only particles we know of, that annihilate one another, are anti-particles. The primary example is an electron and a positron. These particles are easy to get into close proximity. They attract one another because they possess opposite electrostatic charges. Ordinary matter consists of electrons, neutrons, and protons. Neutrons and protons are located together in the atomic nucleus. Electrons are located in “clouds” around the nucleus. Each electron fiercely repels every other, just as each atomic nucleus fiercely repels every other. The repulsion is fierce because it is based on the electrostatic force that is vastly stronger than the force of gravity (one followed by 42 zeros times as strong). This force drives nucleus away from nucleus, and electron away from electron.

On the other hand, the electron and the nucleus are attracted with an equally strong force (this is the origin of the phrase opposites attract). Electrons inhabit “probability clouds” around an atomic nucleus. The chances of their being in some places are higher than the chances of them being in other places. One place where they have almost no chance of being is actually touching a nucleus. This is based on the quantum model of the atom, not the simple fact that there is an incredibly large force of attraction between them.

Particles that don’t touch, can’t annihilate each other. Particles that do touch can have some or all of their mass converted into energy. Long before they reached the point of a singularity, particles in a gravitational collapse would be forced into contact with one another. Total annihilation has to be considered as a possibility. If so, it would generate quite a Bang. Certainly one big enough and persistent enough that it might open up its black hole and allow escape.

Experiments that could bear this out, especially ones involving black holes, tend to be inimical to our way of life. But, on a somewhat safer and more limited scale, we have split atoms, we have fused them, and we have both created and destroyed anti-matter. Experiments with black holes are quite a way off for the present. And, until black holes are the subjects of experimentation, they can only be the subjects of speculation, fantasy, or Numination. And, of course, awe—inspired by the extreme danger a black hole would pose to our life form.