Black holes are one of the many things in the universe that scientists still have a muddy understanding about. However, with the incredible advances of technology, we are able to understand more than what we have in the past. Today, the only way to observe these incredible objects are by looking for radiation from the gas surrounding it. What are they? Black holes are no more than a ^3 dead star.
^2 A star that is considered ^3 alive^2 would be our sun. The sun still produces energy by converting hydrogen into helium, thus considered to be ^3 alive. ^2 Once a star has run out of hydrogen, it begins its dying process. The final stage may result in a black dwarf, which is a small cool object no longer radiating energy, or if the star harbors enough mass it could result in a black hole. Black holes are defined as a collapsed star.
The difference between a black dwarf and a black hole is the original mass of the star, which determines whether or not that star will have enough gravitation force to collapse upon its self and form a suction, or to remain as that small cool object, a black dwarf. Why do black holes suck everything in? To understand why material that enters a black hole is unable to escape, one must understand the concept of escape velocity. This is the velocity (speed) at which any material needs to exceed in order to escape from something. Because, as Einstein said, ^3 What ever goes up must come down! ^2 In other words, in order for a space craft to exit the Earth^1's atmosphere so that it must not come down, it must exceed a certain speed.
In order to figure out the Earth^1's escape velocity one takes the square root of the planet^1's mass divided by the planet's radius. PLANET^1 S MASS / PLANET^1 S RADIUS = ESCAPE VELOCITY On Earth with a radius of 6,500 km, the escape velocity would be 11 km / sec. Therefore to launch any object away from Earth, the object must travel (escape) faster than 11 km / sec. All of this is of course the result of gravity. However, imagine a huge vise that squeezed the Earth to one-quarter its present size. What would then happen to the escape velocity?
The velocity would increase because the mass would increase as the radius increased. Thus, taking the square root of a larger number, ending up with a larger number that being the escape velocity. The actual escape velocity of this hypothetical question would double it making it 22 km / sec. Taking a step further, what would happen it the vice were to squeeze the earth to a radius of one centimeter?
The escape velocity would then be 300,000 km / sec, the velocity of light!! This means that if this was to actually happen to our Earth, that not even light would be able to escape from the Earth^1's surface. For stars that harbor such an immense amount of mass, it is possible for the escape velocity to be greater than that of the speed of light (unlike our sun). The gravity of such a large star can literally crush it on all sides until it is shrunken to the size of a house, a room, a pea and so fourth until it is invisible. This is exactly what occurs to a star of such magnitude as it dies and collapses on itself.
Because of the amount of mass within the black hole^1's small area, the escape velocity is so great that not even light can escape. As far as it is known there is nothing that exceeds the speed of light, therefore there is nothing that can escape a black hole. What happens to everything that enters a black hole? The black hole its self it called the singularity. It is the contradiction of matter that contains an infinite density and infinite volume.
Mass and energy within this point are concentrated into a infinitesimal point where space vanishes and time comes to an end. The area directly outside of the singularity is called the event horizon or Schwarzschild radius, after a German theorist. At this edge, matter that goes in will disappear. the size of the even horizon equals three km multiplied by the object^1's mass. (mass expressed in units of solar masses). Here, where the gravitation force becomes overwhelming and the curvature of space-time so extreme, it folds space-time over on itself.
However, the even horizon is not a boundary, but a communications barrier. An analogy helps us to understand this concept. However, it is not complete because one cannot demonstrate it in the forth dimension of time. Pretend that a huge family lives in a town that is on an enormous trampoline or rubber mat. the town decides to hold a family reunion at a given time and place. One person decides not to go. To keep in touch with the family across town, the person communicates by means of ^3 message balls.
^2 In this case, the message ball would represent radio waves traveling at the speed of light across the rubber mat. that represents space time. As the people continue to gather, the sheet begins to sag more and more because of the mass gathering in the one area. the curvature of space-time increases as the mass grows. As it increases, the message balls are being rolled less frequently, as the sheet becomes more sagged. When all the people have arrived, the rubber sheet closes off into a bubble, which compresses them.
The message balls are unable to reach the person that didn^1 t attend. Regardless of the speed of the message balls, they are unable to escape from the outer edge of the bubble, which represents the event horizon of a black hole. Any material entering a black hole is subjected to a great amount of stress caused by the gravity. A person that falls feet first would be enormously stretched in height and width.
Since the gravity would be stronger at his feet, the person would be immediately torn apart after passing the even horizon. Within the collision of the torn up debris, there would be a great deal of friction. The rate at which this occurs is so fast that the friction would happen prior to the submersion below the even horizon, which would emit radiation because of this. The thermal radiation is so hot that it is expected to be x-ray types of radiation.
Once the radiation surpasses the even horizon, the x-rays cease and the material inside continues in great distortion. This is what scientists are trying to link to their observation of such radio active areas within out universe today.
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