what is a blackhole?

Answer 1

A black hole is an object predicted by general relativity,[1] with a gravitational field so powerful that even electromagnetic radiation (such as light) cannot escape its pull.[2]

A black hole is defined to be a region of space-time where escape to the outside universe is impossible. The outer boundary of this region is called the event horizon. Nothing can move from inside the event horizon to the outside, even briefly, due to the extreme gravitational field existing within the region. For the same reason, observers outside the event horizon cannot see any events which may be happening within the event horizon; thus any energy being radiated or events happening within the region are forever unable to be seen or detected from outside. Within the black hole is a singularity, an anomalous place where matter is compressed to the degree that the known laws of physics no longer apply to it.

Answer 2

A blackhole is a black coloured dense material in the universe(1 teaspoon of blackhole weighs almost some million tonnes) which is almost as huge as 40 to 50 times our sun and an extraordinary trapper of light. It is like a thick veil in the sky. The blackhole's trapping of rays is somewhat like an ocean. Like in an ocean, the upper layers of it are only lighted and the lower ones dark. But this is a dense one so at once when the rays are coming, they cannot be illuminated and appear as absorbing the light in it. And this is the reason, this black ocean like object can't let light escape.

Answer 3

A black hole is an object predicted by general relativity, with a gravitational field so powerful that even electromagnetic radiation (such as light) cannot escape its pull.

A black hole is defined to be a region of space-time where escape to the outside universe is impossible. The outer boundary of this region is called the event horizon. Nothing can move from inside the event horizon to the outside, even briefly, due to the extreme gravitational field existing within the region. For the same reason, observers outside the event horizon cannot see any events which may be happening within the event horizon; thus any energy being radiated or events happening within the region are forever unable to be seen or detected from outside. Within the black hole is a singularity, an anomalous place where matter is compressed to the degree that the known laws of physics no longer apply to it.

Theoretically, a black hole can be any size. Astrophysicists expect to find black holes with masses ranging between roughly the mass of the Sun ("stellar-mass" black holes) to many millions of times the mass of the Sun (supermassive black holes).

The existence of black holes in the universe is well supported by astronomical observation, particularly from studying X-ray emission from X-ray binaries and active galactic nuclei. It has also been hypothesized that black holes radiate an undetectably small amount of energy due to quantum mechanical effects. This is called Hawking radiation.

Most planets and other celestial bodies are stable because the Pauli force between electrons prevents atoms from collapsing into each other, while gravity, electromagnetism, and the strong force pull them together. These create a balance which allows material bodies to retain their shape and structure. In extreme circumstances, however, if there is enough matter in a small enough space, gravity ends up winning, and the matter collapses: electrons cannot stay distant from the atomic nucleus, and incredibly dense matter forms (sometimes called neutronium). Eventually, if the star is massive enough, even the Pauli force between nucleons cannot resist gravity and the star collapses into itself further forming a black hole. In a way that can be hard to imagine, nothing can stop this collapse if enough matter gets into a small enough space, and the matter collapses to a point of zero height, width, and depth, known as a singularity, in which the matter is so dense it is no longer "matter" in any real sense, but some kind of anomaly in space. Anything that gets too close to this singularity will also collapse into it the same way, whether it is matter, energy or even light itself, which is the fastest thing in the universe. The failure of even light to escape its gravitation is how the phenomenon initially acquired the name black hole.

Answer 4

Try to jump so high that you fly right off of the Earth into outer space. What happens? Why don't you get very far? You are essentially trapped on Earth, unless you can find a rocket that can travel at escape velocity away from the Earth.
The escape velocity can be calculated in Newtonian gravity by using energy conservation of an object of mass m in the gravitational field of a planet of mass M in D space dimensions. The escape velocity for the surface of the Earth is about 11 km/sec. Notice that's only 37 millionths of the speed of light. Under what conditions would the escape velocity from the surface of some planet or star be equal to the speed of light?
For a planet the mass of the Earth, this distance is only about a centimeter. So if the Earth were less than a centimeter in diameter, the escape velocity at the surface would be greater than the speed of light.
But thanks to Einstein we learned that when any velocity in a gravitating system approaches the speed of light, the Newtonian theory of gravity has to be put aside for the relativistically invariance theory of Einstein. The relativistic formulation of gravity in General Relativity starts with the Einstein equation relating the curvature of the spacetime geometry to the energy of the matter and radiation in the spacetime. The equation can't be written here, 'coz there are certain mathematical symbols which are not permitted in this forum.

Note that an assumption has been made that we are outside the gravitating body in question. If we're outside the body, and the radial size R of the body satisfies R>R(G), then we don't need to know about what happens at coordinate r=R(G) because this metric doesn't apply to r If RR(G) to r But the problem is: such an observer will never, under any circumstances, not even with the most powerful rocket in the world, ever be able to cross back to r>R(G).
In this case, this gravitating body is called a BLACK HOLE, and at the coordinate value r=R(G), there exists something called a black hole event horizon. The EVENT HORIZON is the relativistic geometric expression of the escape velocity becoming equal to the speed of light. Once anything, even light, crosses the event horizon, it can never escape back out to r>R(G) again.
Black holes can be created by the gravitational collapse of large stars that are at least twice as massive as our Sun. Normally, stars balance the gravitational force with the pressure from the nuclear fusion reactions inside. When a star gets old and burns up all of its hydrogen into helium and then turns the helium into heavier elements like iron and nickel, it can have three fates. The first two fates occur for stars less than about twice the mass of our Sun (and one of them will be our Sun's eventual fate). These two fates both depend on the fermionic repulsion pressure described by quantum mechanics -- two fermions cannot be in the same quantum state at the same time. This means that the two stable destinies for a collapsing star will be:

1. a white dwarf supported by the fermionic repulsion pressure of the electrons in the heavy atoms in the core
2. a neutron star supported by the fermionic repulsion pressure of the neutrons in the nuclei of the heavy atoms in the core

If the mass of the collapsing star is too large, bigger than twice the mass of our Sun, the fermionic repulsion pressure of either the electrons or the neutrons is not strong enough to prevent the ultimate gravitational collapse into a black hole.
The estimated age of the Universe is several times the lifespan of an average star. This means there must have been a lot of stars bigger than twice the mass of our Sun that have burned their hydrogen and collapsed since the Universe began. Our Universe ought to contain many black holes, if the model that astrophysicists use to describe their formation is correct. Black holes created by the collapse of individual stars should only be about 2 to 100 times as massive as our Sun.
Another way that black holes can be created is the gravitational collapse of the center of a large cluster of stars. These types of black holes can be very much more massive than our Sun. There may be one of them in the center of every galaxy, including our galaxy, the Milky Way.

Answer 5

A back hole is a small part of the universe in space with a very strong gravitational Field. It has such a strong gravitational field that even fast travelling electromagnetic such as light can not over it. It pulls the waves inside it. nothing is known to escape it once caught in its gravitational field.

Answer 6

A black hole is an object predicted by general relativity, with a gravitational field so powerful that even electromagnetic radiation (such as light) cannot escape its pull.

A black hole is defined to be a region of space-time where escape to the outside universe is impossible

Answer 7

I am sure you have a good idea of what a black hole is,by now.
A black hole is a theoretical entity that is,superficially very logical.
There is no proof that one exists,they can only be inferred
A black hole would contain no space and such an object could not exist in the universe
A black hole would have to constitute an absence of space so it could not exist.

Answer 8

A black hole is an object predicted by general relativity,[1] with a gravitational field so powerful that even electromagnetic radiation (such as light) cannot escape its pull

Answer 9

You know...a hole that's black...

Either that or a star that has exhausted all of it's fuel and is so dense that it collapses in on itself. This implies a density so large that a teaspoon of its matter would weigh something close to 100 million tons on Earth.

Well, either way, after the star collapses, the gravity is so strong that it eventually creates this black hole. So strong, that not even light can escape its grasp, hence the term, "black hole".

Answer 10

A black hole is an object predicted by general relativity, with a gravitational field so powerful that even electromagnetic radiation (such as light) cannot escape its pull.