What is Black Hole?

Question

I want to know what a black hole is?

Please Suggest me some websites.

Answer 1

a black hole is a dead star that has collapsed and it is spinning very fast and its gravity is d**n strong .

it is something like this :

you have a blanket , ask four people to hold the four corners .

you put a metal ball onto the centre of the blanket. the

blanket will bend down right???

no matter how hard the four people pull , you will still see a 'hole' in the centre . that is black hole .

do not underestimate the black hole!!! it can suck in light , the fastest element ( or not now...) in the universe . that's why it is black . a black hole.

now imagine that you and your friend is near a black hole.

your friend gets sucked in but you are still there ( that is not going to happen actually but lets imagine . i mean you will still be there ? not )  then when you see your friend get suck in , suddenly, time stops.

you still see your friend there . why ??

because we see things as light is reflected to our eyes . inthat case, a black hole sucks in all light and no light is reflected so you see time stop!!!

Answer 2

It is a very powerful gravitational force, where it pulls things into it's center, and even light can't escape from it (that's why it is black)

more info:

http://en.wikipedia.org/wiki/Black_hole

Answer 3

It's a star that "died". The star explodes and falls into itself, creating a "black hole". It is a point in space that sucks in everything that comes near. If you get sucked into one you would be squished into a tiny pinpoint weighing a billion tons. Not pleasant. Then the atoms in your body would break apart and you would be virtually, squeezed out of existance.

http://en.wikipedia.org/wiki/Black_Hole

Answer 4

If a black hole could exist it would be a 2 solar mass sphere about 3 km in diameter whose surface gravity was such that the surface escape velocity would be greater than the speed of light.

  Since no electro magnetic radiation could escape the surface it would be invisible.

Answer 5

A black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can escape its pull after having fallen past its event horizon. The term "Black Hole" comes from the fact that, at a certain point, even electromagnetic radiation (e.g. visible light) is unable to break away from the attraction of these massive objects. This renders the hole's interior invisible or, rather, black like the appearance of space itself.

Answer 6

it is only a star that had died and become very small yet concentrated. but its gravity is doubled or tripled that it is so strong that even the light that it emit cannot escape!

Answer 7

Black hole

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Simulated view of a black hole in front of the Milky Way. The hole has 10 solar masses and is viewed from a distance of 600 km.[1]General relativity



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A black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can escape its pull after having fallen past its event horizon. The term "Black Hole" comes from the fact that, at a certain point, even electromagnetic radiation (e.g. visible light) is unable to break away from the attraction of these massive objects. This renders the hole's interior invisible or, rather, black like the appearance of space itself.

Despite its interior being invisible, a black hole may reveal its presence through an interaction with matter that lies in orbit outside its event horizon. For example, a black hole may be perceived by tracking the movement of a group of stars that orbit its center. Alternatively, one may observe gas (from a nearby star, for instance) that has been drawn into the black hole. The gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and earth-orbiting telescopes.[2][3][4] Such observations have resulted in the general scientific consensus that — barring a breakdown in our understanding of nature— black holes do exist in our universe.[5]

The idea of an object with gravity strong enough to prevent light from escaping was proposed in 1783 by the Reverend John Michell[6], an amateur British astronomer. In 1795, Pierre-Simon Laplace, a French physicist independently came to the same conclusion.[7][8] Black holes, as currently understood, are described by Einstein's general theory of relativity, which he developed in 1916. This theory predicts that when a large enough amount of mass is present in a sufficiently small region of space, all paths through space are warped inwards towards the center of the volume, preventing all matter and radiation within it from escaping.

While general relativity describes a black hole as a region of empty space with a pointlike singularity at the center and an event horizon at the outer edge, the description changes when the effects of quantum mechanics are taken into account. Research on this subject indicates that, rather than holding captured matter forever, black holes may slowly leak a form of thermal energy called Hawking radiation.[9][10][11] However, the final, correct description of black holes, requiring a theory of quantum gravity, is unknown.

Contents [hide]

1 Name

2 What makes it impossible to escape from black holes?

3 Properties: mass, charge and angular momentum

3.1 Black hole types

3.2 Sizes

4 Features

4.1 Event horizon

4.2 Singularity

4.3 Photon sphere

4.4 Ergosphere

4.5 Hawking radiation

5 Effects of Falling into a Black Hole

5.1 Spaghettification

5.2 Before the falling object crosses the event horizon

5.3 As the object passes through the event horizon

5.4 Inside the event horizon

5.5 Hitting the singularity

6 Formation and evolution

6.1 Gravitation collapse

6.1.1 Creation of primordial black holes in the big bang

6.2 Production in high energy collisions

6.3 Growth

6.4 Evaporation

7 Techniques for finding black holes

7.1 Accretion disks and gas jets

7.2 Strong radiation emissions

7.3 Gravitational lensing

7.4 Objects orbiting possible black holes

7.5 Determining the mass of black holes

8 Black hole candidates

8.1 Supermassive black holes at the centers of galaxies

8.2 Intermediate-mass black holes in globular clusters

8.3 Stellar-mass black holes in the Milky Way

8.4 Micro black holes

9 History of the black hole concept

9.1 Newtonian theories (before Einstein)

9.2 Theories based on Einstein's general relativity

10 Black holes and Earth

10.1 Black hole wandering through our Solar System

10.2 Micro black hole escaping from a particle accelerator

11 Alternative models

12 More advanced topics

12.1 Entropy and Hawking radiation

12.2 Black hole unitarity

13 References

14 Further reading

14.1 Popular reading

14.2 University textbooks and monographs

14.3 Research papers

15 External links



Name

The term black hole to describe this phenomenon dates from the mid-1960s, though its precise origins are unclear. Physicist John Wheeler is widely credited with coining it in his 1967 public lecture Our Universe: the Known and Unknown, as an alternative to the more cumbersome "gravitationally completely collapsed star". However, Wheeler himself insisted that the term had actually been coined by someone else at the conference and adopted by him as a useful shorthand. The term was also cited in a 1964 letter by Anne Ewing to the AAAS:[12]

According to Einstein’s general theory of relativity, as mass is added to a degenerate star a sudden collapse will take place and the intense gravitational field of the star will close in on itself. Such a star then forms a "black hole" in the universe.

The phrase had already entered the language years earlier as the Black Hole of Calcutta incident of 1756 in which 146 Europeans were locked up overnight in punishment cell of barracks at Fort William by Siraj ud-Daulah, and all but 23 perished.[13]

What makes it impossible to escape from black holes?

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Far away from the black hole a particle can move in any direction. It is only restricted by the speed of light.

Closer to the black hole spacetime starts to deform. There are more paths going towards the black hole than paths moving away.

Inside of the event horizon all paths bring the particle closer to the center of the black hole. It is no longer possible for the particle to escape.[14]

Popular accounts commonly try to explain the black hole phenomenon by using the concept of escape velocity, the speed needed for a vessel starting at the surface of a massive object to completely clear the object's gravitational field. Using Newton's law of gravity it is straight forward to show that if you take a sufficiently dense object its escape velocity will equal or even exceed the speed of light. Citing that nothing can exceed the speed of light they then infer that nothing would be able to escape such a dense object.[15] Of course, this argument has a flaw in that it doesn't explain why light would even be affected by a gravitating body, let alone why it wouldn't be able to escape. Some argue[who?] that in general relativity light is affected by gravity and that indeed the energy required to escape a black hole is infinite. This makes the argument for the attraction of light stronger but still leaves needed explanation.

Two concepts introduced by Albert Einstein help us understand this situation. The first is that time and space are not two independent concepts, but are interrelated forming a single continuum, spacetime. This continuum has some special properties. An object is not free to move around spacetime at will, instead it must always move forwards in time. In fact, not only must an object move forwards in time, it also cannot change its position faster than the speed of light. This is the main result of the theory of special relativity.

The second lesson is the main message of general relativity, mass deforms the structure of spacetime. Loosely speaking, the effect of a mass on spacetime is to slightly tilt the direction of time towards the mass. As a result, objects tend to move towards masses; we experience this as gravity. As you get closer to a mass this tilting effect becomes stronger. At some point close to the mass this effect becomes so strong that all the possible paths an object can take lead towards the mass.[16] That is, no matter how hard you try—even if you used the most powerful rocket available—your path will only bring you closer to the mass; you are trapped. This is precisely what happens at the event horizon of a black hole.

So, to put it succinctly, the reason you cannot escape a black hole is because you cannot move backwards in time (or faster than the speed of light).

Properties: mass, charge and angular momentum

According to the "No Hair" theorem a black hole has only three independent physical properties: mass, charge and angular momentum.[17] Any two black holes that share the same values for these properties are completely indistinguishable. This contrasts with other astrophysical objects such as stars,

Answer 8

A black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can escape its pull after having fallen past its event horizon.  Light emitted from inside the horizon can never reach the observer, and anything that passes through the horizon from the observer's side is never seen again.

http://en.wikipedia.org/wiki/Black_hole

http://www.damtp.cam.ac.uk/user/gr/publi...

http://cosmology.berkeley.edu/Education/...

Answer 9

Black Hole, an extremely dense celestial body that has been theorized to exist in the universe. The gravitational field of a black hole is so strong that, if the body is large enough, nothing, including electromagnetic radiation, can escape from its vicinity. The body is surrounded by a spherical boundary, called a horizon, through which light can enter but not escape; it therefore appears totally black.