The Structure and Mechanics of Black Holes
Created | Updated Oct 19, 2005
Black holes have a structure, mathematically defined, that is logical and simple. Although the Nova television programs will tell you that inside a black hole all of physics breaks down, that is most certainly not true.
When a star goes supernova, most of its outer shell and gasses have been ejected. Even so, the remaining core would mass about 2 - 2.5 stellar masses. As the stellar core no longer has any nuclear fuel, the star is doomed. Gravity swiftly takes dominance. The molecular repuslion of the atoms in the core is no match for the forces acting on them. The core quickly shrinks in size, collapsing toward nothingness. As the core curves spacetime more and more, the light rays escaping from the core are curved more and more, until even the light is caught by the powerful gravity well, and pulled back down. When no light is being emitted, we say that the star has fallen inside its own event horizon, and is lost forever. (See diagram to left)1
When the core becomes a singularity, the precise mathematical structure becomes fully and readily apparent. The singularity is at the center and bottom, of a massive gravity well. The event horizon is not the top of the gravity well; rather, it is the point at which you would have to be traveling faster than light to break free of the gravity surrounding you.
The event horizon is aptly named. As study after study has suggested, the horizon is a physical manefestation of the curvature of spacetime. The event horizon is as good as a solid wall of lead for seperating things. A person on this side of the event horizon could not even see a person on the other side. To our safe observer, the (suicidal?) explorer would seem to suddenly wink out of existance as he crossed the event horizon. No radio transmission or light wave can make it out. Whatever falls inside an event horizon is permenantly removed from the Universe.
The diameter of the event horizon is proportional to the mass of the singularity. If, for example, the singularity was 10 solar masses, the event horizon would be about 60 kilometers (37 miles). Since the event horizon is-to all intents and purposes-the black hole, we say that the diameter of a ten solar mass black hole is 60 kilometers. The chart at right shows the relation of mass to diameter.2
Black holes are amazingly simple: they consist of a singularity and an event horizon. There is nothing else. Everything inside the event horizon has already been compressed into the singularity. Even vacuum is nonexistant. There is simply nothing.
It is also important to note some of the effects of gravity. Since space and time are combined in the spacetime continuum (if you'll pardon the sci fi lingo), gravity acts equally on both. How? Gravity can actually slow time. Yes, its true. Here on Earth, the effect is negligable, and almost non-existant. But near a black hole, the gravity is so strong that the same effect is warped beyond belief. Time actually stops at the event horizon. You could watch someone drift toward the black hole and watch his clocks move slower and slower as he approched the event horizon. This is not because of any effect on the mechanical components of the clocks, but rather because time is measured slower near a black hole. At the event horizon, Time would stop! The person who was going in would not notice a thing, as his heart rate, metabolic rate, respiration, and thinking processes would have been affected to the same exact degree. For him, nothing changes as he crosses the event horizon; he might not even know he had crossed.
Inside the event horizon, everything changes. The person who went in could still see you out there, see the stars and see everything else visible to the naked eye. However, the traveler would find that the directions of space and time were reversed!. Imagine: Here on earth we have the freedom to move in any direction we please. We may not get very far, but we can move in space. Time, on the other hand, drags us kicking and screaming along one path from cradle to grave. Our friend on the other side of the event horizon would find that he could move along the time axis in any direction he wanted. It would do him no good, as the space axis still pulls him inexorable foreward into the singularity.
Although the structure of a black hole is simple (see diagram to left)3, the mechanics are not. I am not qualified to explain them in any detail4, but there are a few things I can explain.
It is important to understand that black holes eat stuff. Everything that goes in is destroyed so thoroughly that not even its basic physical properties remain. Everything that goes in is forever removed from our universe. Since nothing remains of whatever went in, it cannot influence the structure of the black hole. This is best described by Professor William J. Kaufmann, III of San Diego University, who said in his book:
"Suppose you make two black holes. One black hole is make from 10 sollar masses of peanut butter while the other black hole is make from 10 solar masses of bricks. Before gravitational collapse, you have no trouble telling which is which. Peanut butter looks, smells, tastes, and feels very different from bricks. But after the gravitational collapse, it is impossible to tell the two holes apart. Because the infalling matter is separated from us by an event horizon, we have no way of discovering which hole ate the bricks and which hole ate the peanut butter. Since many of the properties of infalling matter are swallowed by the hole, these properties (for example, color, texture, and chemical composition) cannot influence the structure of the hole.
Even though we cannot know what the hole ate, we can figure out how much it ate. By placing a satalite in orbit of the hole, and carefully observing its orbit, we can calculate the total mass of the hole. That number is one of only three numbers on which the structure of the hole depends.
Black Holes of All Kinds
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1For those readers that have not read the first part of this project, there will be a curious lack of anything that even seems to vaguely indicate the presence of a diagram or photo. This is intentional, though not my fault. The publishing company that owns the rights to the images I had wanted to include suggested in a polite way that I not pollute their telephone lines any further or they would remove my larynx. No photos or diagrams will be present because I don't want to drag the guide through any legal mess.2It does not, in fact, show any such thing. This is neither lies nor flim-flammery. See Footnote #1.3You've got the hang of this now, don't you?4You would in fact have to be GOD to fully explain these phenomina, though terrestrial physicists try.
