Some stars are invisible. When you look up the sky on clear night, you may see many blinking points of light. These called the stars. You can see about a thousand stars just by looking up on a clear night. You could also see many thousands more with the use of a small telescope and another billion more with the use of a very powerful telescope. They are really huge balls of bright, hot, glowing gases. They pour out light, just what the sun does, because the sun is also a star. The sun takes up 98 percent of the mass of the entire solar system; 700 million tons of hydrogen is converted into helium ashes.
In the process 5 million tons of pure energy is released; therefore, as the time goes on the sun is becoming lighter. Though scientists keep on inventing stronger telescopes and discovered more stars, there still no one really knows how many stars there are in the sky. The sun is quite small and young compared to others stars. The following are other stars, big and small compared in size to the sun, Proxima Centauri, Sirius B, Arcturus, and Aldebaran. Stars form out of nebulae, condensing slowly over millions of years by the force of their own gravity. Anything that has mass or substance has gravity.
This nebular collapse continues, heating like air in a bicycle pump, until the temperature and pressure in the center are high enough to begin nuclear fusion. The process in its simplest form produces helium from hydrogen and releases enormous amounts of energy. It is this energy heat and light that people feel from the star, the sun, on a sunny day. One of the most remarkable astronomical revelations of our time is the discovery that black hole is existing. But that revelation has left people with equally great questions: What is a black hole? Why the evidences of a black hole still controversial? How does a black hole formed?
What is a Black hole? A black hole is a creation of gravitation. It is so rational to initiate the account of the innovation of black holes at the time of Isaac Newton, who discerned the law of universal gravitation. The law of universal gravitation determines the force acting on absolutely everything. All physical interactions are associated with concrete properties of matter. Newton theorized that light is attracted to massive bodies. It is with this understanding of the fact that light is also subject to gravitational force that the early history of black holes begins, and its history of prediction of their astonishing properties.
Pierre Laplace was a famous French mathematician and astronomer. He was considered as an illustrious personality in the history of science and one of the first scientists, who have a spectacular prediction of one of the properties of a black hole. This theory is to confine light, and thus be invisible. Laplace was not the only person and certainly not the first to arise with this prediction. Similar proposition was made in 1783 in a person of John Michell, a British priest and geologist and one of the founders of scientific seismology. John Michell arguments were very similar to those of Laplace.
Laplace’s paper with the proof of the possibility of existence of black holes was cited in 1973 by the English physics theorists Stephen Hawking and George Ellis in a book devoted to special mathematical aspects of the structure of space and time; Michell’s work was not known to specialist at that time. In1984, the English astrophysicist Martin Rees said at a conference in Toulouse that although what he had to say might not sound to nice in France, the truth was that the first man to predict invisible stars had been the Briton John Michell.
Actually, the prediction made by Michell and Laplace was not yet the true prediction of black holes. Because the point is obviously science of that time did not yet know that nothing in nature is allowed to move at a velocity greater than that of light. This was proved by Albert Einstein in special relativity theory but only in this century. For Michell and Laplace, therefore, the star that they considered was only black since they were not aware that such star loses any chance of communicating with the outside world in any way, of informing the world of any events occurring in the star.
In other words, they could not know that it is not black but also a hole into which one could fall but out of which there was no escape. This is the realization that if light cannot escape from some region of space, then nothing at all can emerge from it; this region is called black hole. Why the evidences of a black hole still controversial? Vachaspati said, “If you define the black hole as some place where you can lose objects, then there is no such thing because the black hole evaporates before anything is seen to fall in,”
(http://www. sciencedaily. com /releases/2007/06/070620115358. htm). Most of what astronomers’ knowledge about the black holes themselves is based on the theoretical models. In any event, research into black holes will continue and it will remains unclear is whether that research will solve the mysteries in bits and pieces or whether it will, with the help of powerful new inventions and technologies; rapidly reveal the secrets hidden in their till then profound depths.
Another reason that detracts from the rigor of Michell’s and Le Verrier’s arguments is that they considered gravitational forces of enormous strength in which a falling body is accelerated to the velocity of light and the emitted light is confined, while at the same time applying Newton’s law of gravitation is not valid for such fields, and developed a new theory, valid for super strong and for rapidly varying fields for which Newton’s theory fails completely; this theory is known as general relativity.
If we want to prove that black holes can exist and to study their properties, it is the theory that we have to use as a tool. A brief outline of some corollaries of Einstein’s theory of general relativity is needed to make understandable the unbelievable properties of black holes. Einstein extended his idea of his model of gravity in his general theory of relativity. He perceived gravitational field as a warping of four dimensional space and time. According to him, large bodies like earth put a dent in space.
Let someone visualize a heavy object on a loosely stretched rubber sheet. The object puts a dent or depression in the sheet. The curvature of the space determines the gravitational effects. The gravitational force near a black hole is so enormous that neither light nor anything can escape from it. Objects such as spaceships, atoms, and molecules, can enter a black hole but can never escape. How does a black hole formed? When the hydrogen is all gone and converted into helium, the star turns into red super giant.
Because of the extreme heat in red super giants, fusion goes beyond helium and undergoes the following process such as: Helium – Carbon – Magnesium – Silicon Iron. After iron, fusion stops, so gravity causes the core to collapse. The iron breaks down into protons and electrons. The protons and electrons merge, producing neutrons, which causes the size of the star to collapse. During the collapse, a shock wave is emitted, releasing particles called neutrons, creating a very gigantic explosion. A supernova is created.
The protons and electrons merge, producing neutrons. This causes the size of the star to collapse down to 30 kilometers across. After the supernova, what remains is neutron core around 30 kilometers across. If the mass is greater than three times to the sun, the star collapses even further. At this point, gravity is so strong that even light cannot escape, thus what is seen here is just a black area. This black area with a large gravity would attract everything to it, like falling in a hole. The neutron star collapses, creating black hole.
Conclusion Black holes are among the most alluring objects in the universe, and they create phenomena that are beyond doubt peculiar. Nowadays, astronomers’ suspect that millions of black holes populate the Milky Way, and these black holes come in a variety of masses and sizes. Super massive black holes can swallow entire stars and accelerate stars that orbit them to great speeds. Rotating black holes pull the space around them as they spin speedy, so that space itself is whipping around at a large fraction of the velocity of light.
Black holes are found incredibly dense. It has powerful gravitational forces and one of the main characteristics of a black hole is its event horizon where in this region of a black hole the gravitational force is so intense that nothing could ever escape even light. According to physicists and astronomers, black holes are formed when huge stars collapse in on themselves at the end of their lives. Black holes exist at the centers of galaxies, where they act as huge engines that drive the motion of stars, according to astronomers.
On the other hand, studying them is tremendously difficult, mostly because in astronomy one can only study the information carried by light. Some astronomers say black holes’ surface is not solid. This surface is called the event horizon and it represents the distance from the black hole’s singularity at which the escape velocity parallels to the velocity of light. Anything that passes through this horizon is trapped inside the black hole. If the sun in fate becomes a black hole, planets that are revolving around it will certainly experience sudden changes because of its gravitational force.
A black hole’s surface gravity is stronger than that of a normal star because all of its mass has been squeezed into an almost infinitely small point. But according to a research, the sun will not become a black hole because it is not massive enough. References Case Western Reserve University (2007, June 21). Astronomers May Have Solved Information Loss Paradox To Find Black Holes Do Not Form. ScienceDaily. Retrieved May 1, 2008, from http://www. sciencedaily. com /releases/2007/06/070620115358. htm