Black Holes

Background information, and evidence that black holes exist

Black holes do exist. They dwell in the nearest and farthest reaches of space. Some of them are large in mass, and some are small, but they all share one trait: density. Scientists use this factor, among others, to locate them. Once the scientists have located the black holes, they can start to study them and unlock their secrets.

Black holes themselves cannot be seen or heard. They are silent, and perfectly camouflaged against the blackness of space. This makes it difficult for scientists to directly see them. Instead, they have to see how a black hole's mass affects the matter around it. The physical evidence is indirect up to this point. The only way for scientists to physically prove that black holes exist (beyond a shadow of a doubt) is to send someone into a black hole. The only problem with that is that he or she would never return. Once any form of matter passes beyond the event horizon it is condemned to remain in a prison with no walls or bars, only the gravity to hold matter in.

Past the event horizon, scientists can only guess at what lies beyond. After that, the quantum laws, and the theory of relativity, cease to exist. Under those conditions most laws of physics don't apply. At the point of singularity, constants become variables, and space and time merge to form an infinitely dense core. (Hawking, 96)

One other thing that can describe the absolute power of a black hole is its effect on light. The reason a black hole is "black" is because nothing can escape its gravity, not even light. (Smith, 2) To escape a black hole's gravity, a piece of matter of energy would have to move faster then the speed of light. If a person wanted to go the speed of light, the first thing his friend should tell him is that it is simply impossible. (Science Odyssey, part 2)

Light travels at a speed of 186,284 miles (299,792 km) per second (Harris/Hemmerling, 422). If an object were to move at the speed of light, the mass of that object would become infinite, and time would stand still for that object. Of course, there would be an incredible amount of friction, and the object would likely explode before it reached the desired speed. On the other hand, since we have never been able to reach the speed of light no one knows what really happens. (Science odyssey, part 2)

Background

Black holes exist in four dimensions. They exist along an x-axis, a y-axis, a z-axis, and the fourth dimensions of time. These four dimensions make up what is known as space-time. All matter affects the curvature of space-time. The denser, the more space-time is curved around it. This is what gives a black hole its power. It puts such a large dent in space-time that everything else is warped toward it. (Hawking, 88)

The first person to mention black holes was a Cambridge don by the mane on John Michell. This was in 1783. His theory was the same, but John Wheeler did introduce the term "black hole" until 1969. It was not until Einstein discovered that light was affected by gravity that anyone did any serious research. (Hawking, 81)

Most of the information on black holes has been discovered within the last twenty years. Many mathematical equations have been developed regarding black holes. They have unfolded how space-time reacts to mass mathematically. This is, perhaps, the best evidence that black holes can exist. Then if a person regards the physical evidence, it makes the theory of black holes quite plausible.

Black holes are "black" directly because of their enormous mass and density. If a star with the same mass as our sun were squashed down until its diameter was 4 miles, it would have the density to be a black hole. (Haybron, the plain dealer) Of course, the star has to have a much greater mass for it to naturally form a black hole. It would have to have about three times the mass of our sun. (Hawking, 96)

For a star to become a black hole, it has to become a victim to a huge implosion. What could cause that to happen? When a very large star runs out of fuel (hydrogen), its outer layers are blown out in a violent explosion. That is called a supernova. When the outer edges are blown out the core is condensed into a black hole, a neutron star, or a white dwarf. (Smith, 4)

Density is the deciding factor, and mass and volume are the factors that make density. If the mass were not critical (mass that is necessary to create a black hole), the star would become a neutron star. A neutron star is a cold star that is supported by the exclusion principle repulsion between neutrons and protons, hence the name neutron star. An average neutron star would have a radius of ten miles or so and a density of hundreds of millions of tons per cubic inch. (Hawking, 84)

If the mass were less than the critical mass needed to form a neutron star, the star would become a white dwarf. If a stars mass is less than the Chandrasekhar limit, it will settle to the density of a white dwarf. The white dwarf would have a radius of a few thousand miles and a density of hundreds of tons per cubic inch. (Hawking, 84) Most likely our sun will become a white dwarf at the end of its life. (Hawking, 96)

Physical Proof

In recent years telescopes have become more powerful. They have allowed scientists to peer into the vastness of space with ever increasing clarity. This allows them to study the movement of stars. Specifically, they let scientists observe how other celestial bodies, like black holes effect stars. (Smith, 6)

One example is named V404 Cygni. Calculations suggest that this particular star is revolving around an object twelve times the mass of our sun. The only problem with this fact is that this star's "dark partner" cannot be seen. There are more that thirty other cases where a light-emitting star is circling an invisible mass just in the Milky Way galaxy. There are probably many more like that in other galaxies. If there are that many that have stars circling them, how many don't have visible stars circling them? There may be some much closer to our solar system. If a person considers how many we can find in our galaxy, and how many that are probably out there that we haven't found, and how many more there are in other galaxies, there is, most likely, a large number of black holes in the universe.

Another one like that is Cygnus X-1. When it was discovered, some scientists thought it was revolving around a very small, but visible star. When scientists took a closer look, they found that there was also a great deal of radiation coming from that location, a tell tale sign of a black hole. In 1975 the scientists made a small bet with their friends that it was in fact a black hole. They were about 80% sure that it was a black hole. Now, they are 95% sure, but that 5% is still too much to know for sure who won the bet. (Hawking, 94)

Another bit of physical proof is the large amounts of radiation given off by the matter as it spirals into the black hole. (Namowitz/Soaulding, 387) Since nothing can escape a black hole's gravity this creates a minor problem in regards to the theory of black holes. The only way to make this fact fit into the puzzle is if the theory of general relativity, and quantum mechanics only function around black holes when light has a shorter wavelength. The radiation is in the form of X rays, and gamma rays, both forms of ultraviolet light. (Hawking, 112)

An "average" black hole emits energy at a rate of ten thousand megawatts. (Hawking, 108) When scientists calculated how many black holes there should be with the given amount of gamma ray background, they found that there are about 300 black holes per cubic light year. (Hawking, 109) A cubic light year is a large volume of space, and it would only make up one millionth of the matter in the universe. To put it in perspective, if they were one million times more common the closest one would probably be about as far away from us as Pluto. (Hawking, 110)

Another problem with the use of radiation to find a more accurate number of black holes is the absence of observable black holes. Only if the early universe was very smooth and uniform with high-pressure can one explain that relative absence of black holes. (Hawking, 110)



One theory is the early universe originated from a gigantic black hole that, when all of the surrounding matter had been consumed the point of singularity exploded outward to form our universe. This would have been the big bang. Before the explosion the point of singularity was, no doubt, under great amounts of pressure. Once the explosion occurred the pressure decreased and the matter expanded out to create our universe. It is highly doubtful that our universe expanded in perfect symmetry. This would suggest that there are more black holes that these calculations allow for. (Smith, 1)

A small bit of information that also adds to the likelihood of black holes existing, is that recent research that suggests that scientists might be able to produce a black hole. They would have to strip gold nuclei of their electrons and shoot them through a tube of 1,740 super-conducting magnets at a speed of 99.95% the speed of light. (Haybron, the plain dealer)

They can do all of this, but many scientists say that mass would be the problem. When the gold nuclei collide they have to produce temperatures of one trillion degrees. This would be hot enough to "melt" protons and neutrons. This would liberate the quarks and gluons that make them. Scientists do not believe that such a small mass could create such high temperatures, so that possibility is "not plausible." (Haybron, the plain dealer)

With all of these calculations, constants becoming variables, and the laws of quantum mechanics ceasing to work under the conditions in or around a black hole, there leaves much to be desired in regards to the perfection of this science. Black holes can exist according to math, and they remain the most likely answer to the fact that there are stars circling celestial objects many times more massive then they are. With further study the properties of black holes will become clearer, and then the theory of black holes will become a proven scientific fact.

Glossary

Big bang: The singularity at the beginning of the universe.

Black hole: A region of space-time from which nothing, not even light, can escape, because gravity is so strong.

Chandrasekhar limit: The maximum possible mass of a stable cold star, above which it must collapse to a black hole.

Event Horizon: The boundary of a black hole.

Gamma ray: Electromagnetic waves of very short wave length, produced in radioactive decay or by collisions of elementary particles.

General Relativity: Einstein's theory based on the idea that the laws of science should be the same for all observers, no matter how they are moving. It explains the force of gravity in terms of the curvature of a four-dimensional space-time.

Light Year: The distance traveled by light in one year.

Mass: The quantity of matter in a body; its inertia, or resistance to acceleration.

Neutron star: A cold star, supported by the exclusion principle repulsion between neutrons.

Quark: A charged elementary particle that feels the strong force. Protons and neutrons are each composed of three quarks.

Singularity: A point in space-time at which the space-time curvature becomes infinite.

Space-time: The four-dimensional space whose points are events.

Wavelength: For a wave, the distance between two adjacent troughs or adjacent crests.

White dwarf: A stable cold star, supported by the exclusion principle repulsion between electrons.

X ray: Electromagnetic waves slightly longer in wave length then gamma rays

Sources

Harris, Norman C., Edwin M. Hemmerling. Introductory Applied Physics. New York: McGraw-Hill, 1980.

Hawking, Stephan W. A Brief History of Time: From the Big Bang to Black holes. New York: Bantam, 1998.

Haybron, Ron. "Creating our own black hole is far-fetched" The Plain Dealer August 29,1999: L5.

Namowitz / Spaulding. Earth Science, New York, Perkins, 1997.

Schwarzschild, Karl. "Schwarzschild Geometry", File:///A|/schwp.html, 3/14/00.

Science Odyssey, The. Part 2, PBS. WNET, New York. 1995.

Smith, Dr. Richard. "Black Holes: The Ultimate Abyss". file:///A|/story.htm, 3/14/00.

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