Tuesday, March 23, 2010
"Black Holes in Space" from Edcon Publishing.
Some things you will read about: Light year; the distance that light travels in one year. Neutron star; a dead star whose atoms have been squeezed into a very dense fluid. Supernova; an explosion in which a star suddenly flares to many times its former brightness. We do know that black holes exist. However, we can only speculate about their exact composition and function.
Every person aboard is a thorough professional who has spent years in training for this mission. So far everything has gone exactly according to plan. Yet, as we approach our target, the black hole Entram X-14, profound anxiety is felt in every corner of the starship. We know that the gravity of Entram X-14 will suck us down, down into its depths, where no human has ever been before. We know we may be trapped forever in a place where time, or even death, does not exist. Or, if all goes well, we may totally disappear from our universe, to emerge from the other end of the black hole in some other alien universe.
Terms such as "stars hip," "black hole," and "alien universe" place us squarely in the pages of a science fiction novel or the latest space movie. Or do they? The fact is that serious astronomers have come up with theories just as fantastic as anything in the movies.
Stars can be described as huge hydrogen bombs in a state of continuous explosion. Each may consume billions of tons of hydrogen per second, yet continue to shine for billions of years. There must come a time, however, for every star when its hydrogen runs out. Setting out to analyze what happens then, scientists have concluded that stars do not all die the same way.
Most of the stars in our universe will die slowly in definite, dramatic stages.
As the hydrogen reaches a certain level, the star first expands to become a "red giant." Ages later, it pulls together again, shrinking down to a "white dwarf." Our sun, billions of years from now, will expand as a red giant, beyond the orbits of Mercury and Venus, then shrink to a white dwarf no larger than its own planets.
Finally, the very last of the hydrogen gone, the dead star will become a "black dwarf": a small, cold object in the vast void of space.
As old as our universe is, it is not yet old enough to contain any black dwarf stars, but enough red giants and white dwarfs have been studied to confirm the theory. All matter is made up of atoms, which are in turn made up of even smaller particles. Because they are microscopic in size, we seldom realize that atoms, like the universe itself, consist mainly of empty space. The parts of the atom move about in a void which is, by comparison, huge. In the formation of a white dwarf, these particles are simply squeezed more tightly together than they were before.
Some stars are many times larger than our sun. The intense heat at the center of such a star causes a rapid and tremendous explosion, a supernova. In one day, a star becoming a supernova will increase to billions of times its former brightness. Then it contracts with fierce speed, smashing its atoms to a kind of soup.
The result is a neutron star, enormously heavy for its small size and difficult to detect by telescope. Some years after this theory was worked out, advanced equipment picked up signals which exactly matched those that had been predicted. So, scientists were able to confirm the existence of neutron stars.
The very largest stars presented still another problem. The laws of science suggested that once these most massive stars began to pull inward, they wouldn't be able to stop at the white dwarf or neutron star stage. In fact, they might not be able to stop at all. The profound pull of gravity on so large an object contracting with such force should cause that object to continue collapsing forever. Such a situation goes beyond the edge of human experience. We cannot imagine an object which has no surface at all, but which contains all the mass and gravity of a giant star. We cannot really picture in our minds this black hole in space.
The gravity of a black hole would be so powerful that nothing which came near could elude it. The more matter it sucked in, the stronger it would grow, so that it could, in time, "devour" neighboring stars or groups of stars. At the very end, the entire universe could consist of one eternal black hole. One theory holds that this has already happened, and that our whole universe is really inside a giant black hole!
Nothing can escape from the gravity of a black hole, not even light. So, having put forth the probability that such things exist, astronomers were not going to be able to find one by ordinary means. The black hole would allow no signal of any kind to escape. On the other hand, matter in the act of being pulled in, should give out a last frantic burst of X-ray before disappearing. On this fact, scientists based their hopes of identifying an actual black hole in space.
Certain strange sources of X-ray have already been discovered. One in particular, Cygnus X-I (pronounced Sig-nus,) seemed promising, but more facts were needed to confirm the belief that it was a black hole. Those facts finally arrived in 1971 via the X-ray detecting satellite, Uhuru, launched from the African nation of Kenya two years before. Once scientists were able to analyze Uhuru's findings, they knew that Cygnus X-I was, in fact, a black hole in space.
In 1978, a second black hole, Scorpii V -861 (pronounced Scorpi,) was identified. There is a strong probability that many others will be added to the list as new and better methods of finding them are developed. Hard facts about black holes elude us almost as successfully as black holes themselves, and scientific reasoning leads us to theories stranger than any we could imagine. Physical laws worked out by Einstein and others prove that gravity has an effect on time and space. Taken to its absolute limit, in the center of a black hole, total gravity would cause time and space to cease existing. The laws of science, as we know them, would no longer apply.
Having accepted that, we open the door to all kinds of speculation. We know that everything in its vicinity is sucked into a black hole, and nothing ever comes out. That matter disappears forever. But where does it go? Nothing comes out of a black hole, at least not the same way it went in. Some scientists suggest, though, that there may be an exit after all, at the other end. Matter may pass through a black hole and come out somewhere else, light-years away. Or it may come out in a completely different universe. In fact, there may be billions of universes at the far ends of our black holes.
Since time actually ceases to exist in them, black holes could also act as time tunnels. It might be possible to travel through them into the distant past or future. Entering a black hole, matter will collapse into a state beyond our understanding. Emerging, though, it could simply expand again to normal size and shape to find itself in another time, another place. Scientists have other dreams as well. Huge amounts of energy are released by every object pulled into a black hole. If we could harness a small black hole and put it into orbit around the Earth, we could feed it anything at all, and the result would always be energy. Catching one, of course, would be a difficult trick. But where black holes are concerned, it may be that nothing is really impossible.
1. A black hole is a _____
2. If an extremely large and nearby star burned out tomorrow, the earth _____
3. According to the selection, which of the following is not a characteristic of a black hole?
4. Stars ______
5. Atoms are mostly made up of _____
6. Once you are inside a black hole, ________
7. Ages after a star shrinks to a white dwarf, it ________
8. Scientists are able to locate black holes in space by using ______
9. Another name for this selection could be _______
10.This selection is mainly about _______
A very good explanation of Black Holes by Stephen Hawking. He makes it very clear and easy to understand.
A Youtube Video: Mysteries of Deep Space: Black Holes.
For more on this subject, read "A Planetarium is a Theater".