Does blackhole exist..??

Question

Please answer...

Answer 1

Since the Hubble Space Telescope was launched in 1990, there have been many observations of what are believed to be black holes, including the photograph below of a suspected black hole in the heart of the galaxy NGC 6251.
But the study of black holes began in theoretical physics long before there were any observations of these objects by astronomers. Not just an interesting physical phenomenon, black holes are extreme geometrical objects with fascinating mathematical properties that have posed serious challenges to the foundations of classical and quantum physics.

Black hole geometry:
What makes a black hole so special is the extreme effect it has on the propagation of light. Suppose we have a black hole spacetime described in general relativity by some set of coordinates {xa} and some metric tensor gab. The paths of light rays are described by null (i.e. lightlike) geodesics, which are computed using the geodesic equation.
The possible transverse (orthogonal to the propagation direction) deformations of a bundle of null geodesics can be reduced to three types: the expansion q, rotation wab and shear sab, computed as the trace, antisymmetric part and symmetric part, respectively, of the covariant derivative of the geodesic tangent vector.Taking the derivative of the expansion q along a null geodesic leads to what is called the focusing equation.If we're in a spacetime with no rotation, and the matter and energy density is positive, then we arrive at a very important inequality for q that is the key to all the mysterious and interesting properties of black holes.
According to our sign convention, if q is negative, it means the light rays are being focused together instead of spread apart by the spacetime geometry. The above inequality tells us that once light rays start being converged by gravity with some value q0<0, then in a finite distance along the light ray, nearby light rays will be focused to a point, such that they cross each other with zero transverse area A.
This is bad news if these light rays all emanated from a single source, because it means the light is being infinitely focused into a singularity, and the concept of a geodesic has broken down. When q turns negative for both "incoming" and "outgoing" light rays, it means that the light has been trapped, that the escape velocity from that gravitational field has become greater than the speed of light.
When q is zero or negative for both incoming and outgoing null geodesics orthogonal to a smooth spacelike surface, that surface is called a trapped surface, and any closed trapped surface must lie inside a black hole. This an abstract general definition of a black hole that is independent of any coordinate system used to describe it. Gravity bends light like a lens, and a black hole can be thought of as a very peculiar type of lens, one that bends light so that it can never be seen.
Black holes have four very important properties which have become known as the Four Laws of Black Hole Physics of classical general relativity.

The Four Laws of Black Hole Physics:

0. The surface gravity k at the event horizon is constant: it has the same value everywhere on the event horizon.
1. The change in mass of a black hole is proportional to the surface gravity times the change in area.
dM = (k/8p) dA
2. The surface area of the event horizon of a black hole can only increase, never decrease. (This means that two black holes can join to make a bigger black hole, but one black hole can never split in two.)
3. It is impossible to lower the surface gravity k at the event horizon to zero through any physical process.

Note that according to the second law property, it is impossible for black holes to decay and go away, because a black hole cannot get smaller or split into smaller black holes. This is going to be changed when we add quantum mechanics to the theory in the next section.
If these laws look familiar somehow, there's a good reason. This is a tremendously important similarity that will also be discussed in the next section.

The Singularity Within
The problem with the type of focusing of light that defines the presence of a black hole is that once it starts, the focusing equation says that it ends in utter disaster. Once a bundle of null geodesics becomes trapped by crossing to q<0, within a finite distance along each geodesic, q> -Infinity, the geodesics will cross at a point, and the transverse area of the bundle will go to zero. When this happens, the necessary conditions for the existence and uniqueness of these geodesics are violated, and it's no longer possible to use the geodesic equations to predict what happens to the geodesics after they cross.
The spacetime will then exhibit one of the two possible behaviors:
1. The spacetime curvature in this region remains finite for all observers, but notion of predictability for the spacetime breaks down, and evolution of the spacetime can no longer be uniquely predicted from a set of initial data.
2. The spacetime curvature in this region becomes infinite for all or some observers, so that there simply is no possibility of extending geodesics past the point where they cross, they simply end there. The spacetime as a whole retains its predictability but the region contains a spacetime singularity where the paths of observers simply end their existence, and spacetime itself can no longer be defined.

Is there a Cosmic Censor?
So gravity can focus light so powerfully that it can spontaneously end the existence of observers, destroy the definition of the spacetime itself, or spoil the unique time evolution in a spacetime based on a sensible set of initial data? What is to protect us then from the pathological possibilities of strong gravitation fields?
The Cosmic Censorship Conjecture proposes that in the context of the theory of general relativity, in a spacetime where the total energy density is positive, pathologies such as spacetime singularities and breakdowns in causality and predictability are always hidden behind the event horizons of black holes.

Answer 2

Yes very much. Your question, questions the existence of blackhole. First let me clear you that blackhole is not an imaginary term.

Blackholes are refered to burnt out stars. you might know that every star has some (rather tons and tons of) fuels - mostly helium - to support its nuclear reaction. And a blackhole gets former when a star losses all its fuel and there is no further fuel to support its reaction.

At this stage, the star turns out to be a thing that is left with MASSIVE magnetic (or gravitational) force. It absorbs all the things that is near to it and it is invisible. As it absorbs the bodies (planets, asteroids etc..,) it grows in its size.

It is invisible because it even absorbs the light getting into it (think of its massive magnetic force).

There are more about the blackhole and it is not fully uncovered...

The following links will be useful for you to know about blackhole and its existence.

Answer 3

A black hole is a celestial body so dense that light cannot escape its gravitational pull. It is formed when a star's gravity causes it to collapse into itself. Usually, pressure caused by heat from burning up hydrogen and other fuels balances out the star's gravity. However, when the star runs out of fuel, it is overcome by gravity and proceeds to collapse. A smaller star, with a mass less than one and a half times that of the sun, becomes a white dwarf. A star with a mass more than one and a half times that of the sun becomes a neutron star or, if it is massive enough, it collapses to a small point of great density-a black hole. Because of its large mass, the black hole has a gravitational pull from which even light cannot escape. Light rays passing near the black hole are bent, and if they come close enough they are sucked in or trapped in orbit around the black hole. The trapped light rays define the event horizon of the black hole. The event horizon is the boundary past which nothing can escape from the black hole. Approaching the event horizon, time seems to slow down. A gravitational redshift occurs, as light turns red because it loses energy trying to escape from the black hole. Inside the event horizon, predictability and the laws of science break down in the presence of a singularity, or infinite curvature of spacetime. Because of its infinite density, the singularity causes all time and space to be the same. Meanwhile, the tidal forces, where the gravitational pull of the singularity is stronger closer to it than further away, tear matter apart as it nears the singularity. So the answer to your question is no

Answer 4

Yes. The most obviously visible is the Tottenham Hotspur midfield. Great players go in and are never seen again outside the third division.

Answer 5

It definitely does - we just can't see it. A black hole sucks everything within its horizon line including light. Scientist still don't know what is beyond a black hole. The only reason we know it exists is that astrologers noticed a place where there was no light.

Answer 6

Yes black holes really exists.........

http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html

http://amazing-space.stsci.edu/resources/explorations/blackholes/

visit this site you may get some idea.....

Answer 7

Yes! It does. Black holes exist. The holes have been gathered by measuring gravitation disturbances in gravitating bodies.

Thave also been xrayed.

Answer 8

yes Black holes form when very massive stars runs out of fuel.

Answer 9

No, black holes do not exist.
A black hole is a logical theoretical entity but a deep analysis of it"s working characteristic make it a non-viable entity.

Answer 10

yes