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Definition of black hole
1 Meaning of black holeA black hole or black hole is a finite region of space inside which there is a concentration of high enough mass to produce a gravitational field such that no material particle, not even light, can escape from it. However, black holes may be capable of emitting radiation, which was guessed by Stephen Hawking in the 1970's. The radiation emitted by black holes as Cygnus X-1 does not come however own black hole, but his record of acreccion.
The gravity of a black hole, or «curvature of space-time», causes a singularity wrapped by a closed surface, called the event horizon. This is provided for by the Einstein field equations. The event horizon separates the region of the black hole from the rest of the universe and is the boundary of the space from which no particle can leave, including photons. This curvature is studied by general relativity, which predicted the existence of black holes and was their first indication. In the 1970s, Ellis, Hawking and Penrose showed several important theorems about the occurrence and geometry of black holes. Previously, in 1963, Roy Kerr had shown that in a four-dimensional spacetime, all black holes should have a quasi-spherical geometry determined by three parameters: its mass M, the total electric charge e and its angular momentum L.
Guessed in the center of most galaxies, including la Vía Láctea, black holes there supermasivos.5 the existence of black holes is supported by astronomical observations, in particular through the emission of x-ray binary stars and active galaxies.
2. Definition of black holeThe concept of black hole has a recurrent employment in the field of astronomy and is used to designate the region belonging to the space of finite characteristics and in which, in its interior, a mass high, capable of generating a gravity field is concentrated in which no particles of a material nature, including in the lightYou can escape from it.
The gravitational field is a field type in which the forces of gravity are represented. It should be noted that this region is able to emit radiation.
The aforementioned gravity generates a particular matter which is known as the event horizon. The event horizon, also known as event horizon, consists of a hyper surface of frontier of space and time in which the events that occur on one side of it may not ever affect an observer who is on the opposite side.
The physicist and British scientist Stephen William Hawking was one of the more they contributed in respect of this issue of the spatio-temporal uniqueness and also was the first to talk about the emission of radiation into the black hole. He has even written a book, which was published in 1988, history of time: from the Big Bang to black holes, which precisely addresses the issue of the formation of black holes with thoroughness. For instance, anyone who wants to know more in detail this subject can resort to this text.
According to the studies conducted by Hawking and other scientists, believed that in good part of the galaxies, including the milky way, there are black holes.
Meanwhile, in terms of its origin, considered that the black hole is the result of a gravitational collapse which started after the death or exitincion of power, a red giant, as it refers to a star of a huge mass.
After millions of years of life the gravitational force of this huge star will exert much force on it that will cause a very concentrated mass and will become a white dwarf, in such as are called the body sapping his energy. Meanwhile, in this phase it is possible to collapse and that this dwarf becomes the mentioned black hole.
3 Concept of black hole
What is a black hole?To understand what is a black hole, let's start with a star like the Sun. The Sun has a 1.390.000 km diameter and a 330,000 times Earth's mass. Taking into account that mass and the distance from the surface to the Center shows that any objects placed on the surface of the Sun would subjected to a gravitational attraction 28 times higher than terrestrial gravity on the surface.
A current star retains its normal size due to the balance between a high core temperature, which tends to expand the stellar substance, and the massive gravitational pull, which tends to collapse it and squeeze it.
If at a given time the internal temperature drops, gravitation will be mistress of the situation. The star begins to contract and throughout that process disintegrates the atomic structure of the interior. Instead of atoms have electrons, protons and neutrons loose now. The star is still contracting until the moment in which the mutual repulsion of the electrons counteract any further contraction.
The star is now a "white dwarf". If a star like the Sun suffered this collapse that leads to the State of white dwarf, all its mass would be reduced to an area of about 16,000 kilometers in diameter, and its surface gravity (with the same mass but much less than the Center) would be 210,000 times greater than Earth's.
Under certain conditions the gravitational pull is too strong to be counteracted by electronic repulsion. The star shrinks again, forcing the electrons and protons combined to form neutrons and also forcing the latter to bunched in close contact. The neutron structure then counteracts any further contraction and what we have is a 'neutron star', which could accommodate all the mass of our Sun in a field of only 16 kilometers in diameter. The surface gravity would be 210.000.000.000 times higher than the one we have on Earth.
Under certain conditions, gravitation can overcome even the resistance of neutron structure. In this case there is nothing that can oppose the collapse. The star can contract until a zero volume and surface gravity increase towards infinity.
According to the theory of relativity, the light emitted by a star loses some of its energy to move forward against the gravitational field of the star. The more intense is the field, greater is the loss of energy, which has been experimentally tested in space and in the laboratory.
The light emitted by an ordinary star like the Sun lose very little energy. The emitted by a white dwarf, somewhat more; and the emitted by a star of yet more neutrons. Throughout the process of collapse of the neutron star comes a time in which the light emanating surface loses all of its energy and cannot escape.
An object subjected to one better compression than the of neutron stars would have a gravitational field so intense, that anything that is exacted to it would be trapped and could not return to exit. It is as if the trapped object had fallen in an infinitely deep hole and not evidently never fall. And as not even light can escape, the compressed object will be black. Literally, a 'black hole'.
Today astronomers are finding evidence of the existence of black holes in different parts of the universe.