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Black holes are very mysterious thing which is found in space. Black hole is such a thing which attracts every thing towards it's self and after taht nobody knows that where is the thing which is attracted by black hole. According to Scientists black hole is a thing have a very high capacity of attraction.
Discovery:-
In 1916, the German astronomer Schwarzschild, with the support of Einstein's works, calculated the size of a star whose escape velocity would be equal to the speed of light .
This speed is an absolute limit, and according to relativity, nothing can go faster.
What's more, we know that the size of a neutron star decreases when its mass increases, because gravity becomes stronger than the degeneracy pressure.
If the mass of such a star increases, there comes a time, called the Oppenheimer-Volkoff limit, when the escape velocity becomes equal to the speed of light, and nothing will be able to escape the star.
Let us notice that the cohesion of a neutron star is also depending of the strong nuclear interaction. As the behaviour of this interaction is poorly understood under a high gravity, the Oppenheimer-Volkoff limit is not precisely known. It is contained between 1.5 and 3 solar masses.
If nothing, not even light, can't escape, this star becomes invisible : Such an object is called a black hole.
The black hole has no material surface ; the original matter of the star is shrunk to an infinitely dense point, called a singularity.
The "surface" of the black hole is called the horizon, its size is called 'Schwarzschild radius'.
If G is the gravitational constant and M the mass of a body whose radius is R, the escape velocity is
. In the case of a black hole, this velocity is equal to c the speed of light,
hence the Schwarzschild radius of a black hole is expressed as
You can watch more about Black Holes in the following videos:-
Some lines of this article is copied by:-http://nrumiano.free.fr/Estars/b_holes.html
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