Black Holes

.. stence. The singularity, to some scientists, is nature’s way of saying that the present physical laws we are using are not adequate to cope with the situation-perhaps we have missed the proper application of some existing laws or, in the extreme, because new laws are needed. Other scientists are just as certain that once we have a black hole, the singularity is ruled out; they indicate that as it takes an infinite time to reach the gravitational radius and as the universe spans a finite time, the black hole simply does not have enough time to go to a singularity. Perhaps an example will serve to illustrate what happens in space-time that could give rise to a singularity. Picture a thin sheet of rubber stretched over a large frame, and let us assume that this rubber represents a corner of the universe.

If we take a ball and place it in the middle of the sheet, the ball will sink into or depress the sheet to deform it. If we replace the ball with a heavier one and place it on the sheet, the ball will stretch the rubber more and the deformation will be greater, with the ball sinking deeper into the rubber. A still heavier ball will deform the sheet more and the ball will sink still farther into the rubber. Finally, if the ball had almost infinite weight and we assumed the rubber sheet could not tear, the ball would drop to an almost infinite distance from the frame Peters 6 supporting the rubber. And if at that instant the rubber sheet did open up a tiny hole, the ball might pop through the tiny hole to escape the sheet.

With the escape of the ball, the pressure on the rubber would be relaxed and it would spring back to its initial position as a flat sheet. The gravitational stress would have been removed from space-time, but the ball would have effectively left our universe. Where would the ball be now? This situation has been deeply explored by many astronomers that we know of today.(Levitt 80-81) To return to our rubber sheet analogy, we can visualize a second rubber sheet directly under the first; as the black hole deforms the top sheet in some mysterious manner the bottom sheet is also deformed as a mirror image of the top. Or one can picture a softly inflated rubber balloon into which one is poking a finger. We will poke a finger in from the other side along a diameter. Now imagine a marble being pushed into the balloon by one of the fingers; the finger coming in from the other side of the balloon just touches it. Further imagine that the marble mysteriously passes through the two distended layers of the rubber.

When the pressure of the fingers is removed, the marble ends up at the other side of the balloon, diametrically opposite to the point where it was introduced. If we imagine the marble to be a black hole in this fashion, we have transferred it to another part of the universe. One serious drawback must be mentioned. At this time one cannot visualize an astronomer being compressed to the densities found within a black hole. However, this should not be considered an impossibility, for this concept possesses many fascinating overtones. One must remember that if we move with the speed of light, Peters 7 time literally stops, dimensions in the direction of motion shrink to zero, and mass becomes infinite. One cannot help concluding that an astronaut traveling at the speed of light would have zero dimension with infinite mass.

There is one difference –The singularity is a point while the astronaut becomes a line at the speed of light. Theory tells us that even though the astronaut was compressed to a line-this is what we on the outside world would see, if indeed it were possible to see him-the fast- moving astronaut would mot notice any difference in shape, motion, or time. This exposition gives rise to a most intriguing thought. Perhaps at some future date, by moving just within the gravitational radius, an astronaut may be able to move to another universe.(Levitt 93-94) Gravitational Collapse is the catastrophic fate that befalls a massive object when it’s gravity completely overwhelms all other forces. During most of a star’s lifetime, it’s tendency to contract as a result of it’s gravity is balanced by the outward pressure produced by the heat of it’s nuclear reactions. Eventually, however, the nuclear fuel will be exhausted. If the star’s mass is less than about 3 solar masses, it will eventually contract to a stable configuration as either a white dwarf (about the size of Earth but hundreds of thousands times denser) or a neutron star (a similar mass compressed into a sphere only a few miles across). More massive stars, however, will continue to shrink even further when their thermal and rotational energy is exhausted.

Unless the star sheds its excess mass, gravity will overcome all conceivable forces and gravitational collapse will occur. Once gravity exceeds the other forces, the star will fall in on itself in a few hours. Peters 8 When the size of the collapsing star falls below what is called the Scharzschild Radius, the escape velocity becomes equal to the light. When not even light can escape from the surface, the star is said to be inside a black hole. Theorems by Roger Penrose and Stephen Hawking show that, according to general relativity and similar theories of gravitation, a singularity or edge to the space-time continuum must occur.

It is believed, but has not been proved, that everything inside a black hole will hit the singularity and be utterly destroyed within a few microseconds; however, some claim that matter and energy may reappear in another universe. The collapse of a star or a dense cluster of stars can release large amounts of energy, perhaps 10% of the total rest-mass energy of the system if the collapse is nonspherical. Most of the energy will probably be emitted as gravitational waves. Matter falling into a black hole already formed can also release electromagnetic energy. This is a possible source of X rays from Cygnus X-1 in our galaxy and of visible light radio waves from quasars and from certain other distant galaxies.

The universe as a whole may also undergo gravitational collapse. The universe is presently expanding as distant galaxies move apart, but if they do no have escape velocity relative to each other they will eventually fall back together and bring the universe to an end. Whether this will happen depends on the density of matter in the universe, which is not precisely known.(Asimov 255) For the past couple of centuries astronomers have done many things to try to unlock the mystery of these natural wonders called black holes. The curiosity of many scientists has motivated them to use every means possible to do this. If there is Peters 9 one scientist who, in the last couple of decades, has contributed more towards this cause, it would probably be Ken Croswell.

He has had something to do with most of the major advances in this field of study. However, even with people like Croswell, our little world is still far from unlocking the mind-boggling mystery of black holes. Science.

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