Black Holes

It was a star vastly larger than our own sun. For hundreds of years this giant star burned brightly in its corner of the universe. Then, at the end of its life span, a strange thing happened. The dying star began to collapse in on itself. While the star was in its death throes, all the matter that made up the star was squeezed together into a smaller and smaller area. Soon the star measured no more than a mile across. Its matter was so tightly packed that a piece of it the size of a small stone weighed as much as a mountain.

As the dead star continued to fall into itself, it brought with it every bit of matter in the area. Every speck of dust, every stray atom, was dragged into it. The star had become a black hole. A black hole is a small area of matter so dense that not even a light beam can escape the pull of its gravity.

Since no light can leave black holes, there is no way for us to see them. They are invisible. We know of their existence because of the strange things that happen around them. Light that is traveling through space just vanishes.

Just how wild is a black hole? Let's take a look at gravity. A common expression related to gravity is, "What goes up must come down." When someone throws a ball into the air, it must return to Earth. This happens because Earth attracts the ball, or pulls it toward itself. A flowerpot that is knocked off a third-story window will always hit the sidewalk. It is only the great thrust of giant rockets that allows the space shuttle to escape the pull of Earth's gravity.

On a planet with double or triple Earth's gravity, objects would act quite differently, because the pull, or attraction, would be much stronger. A ball thrown into the air would not go very high, and it would plunge quickly back to the surface of the planet. A falling flowerpot would be a deadly weapon. It would kill any luckless pedestrian who might happen to get hit by it. Rockets far more powerful than those used on Earth would be needed to break away from the pull of the planet's gravity.

Beams of light, however, would have no trouble at all escaping from this planet. Even if the force of gravity were increased to a million times that of Earth, light beams would still not be affected. Humans on such a world, though, would be crushed flatter than their own shadows.

Only if the amount of gravity were many billions of times stronger than Earth's would light beams bend back to the surface. That is the case with a black hole. It is hard to imagine just how dense and heavy black hole matter is. A penny made from black hole matter would rip through your pocket and plunge through the earth with the greatest of ease. When it emerged on the other side, it would hover in the air for a moment and then plunge back through the earth.

Black holes are the strangest objects in the universe. Nothing ever leaves a black hole. No light leaves it. No physical objects leave it. Once something enters a black hole, it is there forever. Black holes are like permanent detention halls in the sky. If a travel agent were to arrange a flight to a black hole, it would have to be a one-way trip. As the scientist Robert Jastrow said, "It is almost as though the material inside the black hole no longer belongs to our universe."

Suppose, just for the sake of amusement, that you happened to drop into a black hole. What would happen to you? Think of going feet first. Your feet would be pulled down faster than your ears. As a result, you would be drawn into a very thin thread of matter. Then the individual atoms in your body would be pulled apart.

Were you to survive the trip, however, some scientists believe that you would emerge in the fourth dimension. You would be in a totally different universe. The point where matter exits from this universe and goes into the next is referred to as a white hole. Many scientists believe that there are at least five black holes in our section of the universe. But, then, no one really knows for sure. Our knowledge of black holes is based only on informed guesswork.