what do you mean by black hole ?

Answer 1

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

It formed after the death of a star.

Answer 2

A black hole is a very dense dead star that was formed after a brilliant supernova. When stars become old, their future is decided by their mass. If their mass is greater than the Chandrasekhar's limit, the star shrinks within itself and when the pressure becomes very high, the outer layer of the star is thrown into space while its core forms a black hole or a neutron star. They cannot be viewed using an optical telescope as their gravitational force is too high that they absorb light.
According to Albert Einstein, the theory of relativity fails at the centre of a black hole as the curvature of space becomes infinite.
Astronomers believe that the galactic centre of every galaxy has a black hole. But, last year, few astronomers from Europe stated that there is no such thing called black hole and what we have 'observed' are MECo(Magnetically Eternal Compact Object). This theory is yet to be confirmed.

Answer 3

There are and have been over the centuries of civilization many Black Holes - The Black Hole of Calcutta is possibly the most famous one and now we have a Black Hole in space.
Black holes can refer to practically anything real or imaginary

Answer 4

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

Both Newtonian physics and Einstein's general relativity predict the existence of black holes, but:

The Newtonian version incorrectly assumes that photons have rest mass (see History of the black hole concept).
General relativity tells us a lot more about black holes. For example Newtonian physics only explains why an unpowered object cannot escape from a black hole but general relativity also explains why even the most powerful spaceship cannot escape.
Merely having a very large mass is not enough to make a black hole - if it were, most galaxies would be black holes. A black hole consists of mass concentrated into an abnormally small volume. Fortunately Newtonian physics is good enough to explain this fairly accurately:

Newton's shell theorem states that, if the mass of the objects forms spherical shells of uniform density (like a gobstopper or a perfectly spherical onion), you can simplify the calculations by pretending that their masses are all concentrated at their centers of mass. It also implies that the center of mass of such an object is at its geometrical center, which is easy to find. Stars and even planets have their mass distributed in this way because their own gravity forces them to do so, and hence the shell theorem works very well for them and makes calculations much simpler.
The gravitational pull between two objects is inversely proportional to the square of the distance between them (Newton's Law of Gravitation). For example if you halve the distance you quadruple the force, and if you reduce the distance by a factor of 10 you increase the force by a factor of 100.
So a star's or planet's gravitational pull becomes stronger very rapidly as the distance from its center decreases.
In a normal star or even in a neutron star the radius of the outer surface is so large that the gravitational pull at the surface is not strong enough to prevent light from escaping.
So a black hole can only form if a similar mass is compressed into a much smaller radius - so small that the result is not like anything one could reasonably describe as "matter".

Answer 5

A Black hole is an invisible region in space that has an enormous pull of gravity, Caused by a collapsed supergaint.

When the very biggest stars die they form red supergaints. Then they explode into a supernova. However, when they collapse, they shrink so much that they virtually vanish from the universe. They may become what are called - black holes.

Answer 6

black holes are the remnants of giant stars in which the gravitational pull has overcome the expansion power of the star by the fusion reactions.. the star now starts collapsing inwards and its mass density keeps on increasing.
one stage comes wherein the mass density becomes so high that the escape velocity becomes greater than the speed of light.. at such a stage, the object becomes a black hole as no light can escape from its surface.. the object can no longer be observed using spectroscopic techniques and becomes invisible. No material object and not even light can escape its pull then

Answer 7

There are and have been over the centuries of civilization many Black Holes - The Black Hole of Calcutta is possibly the most famous one and now we have a Black Hole in space.
Black holes can refer to practically anything real or imaginary.

Answer 8

The surface of the earth has a gravitational strength such that on object at the surface would have to travel 7 miles per second to maintain an orbit.
Any faster and it would spiral away,any slower and it would crash to the surface.
The surface gravity of a black hole would be such that an object would have to travel at the speed of light to maintain an orbit.
It would have to travel faster to spiral away but it is trapped since nothing can exceed the speed on light.
Since light can't escape it is referred to as a black hole.
A black hole is a theoretical entity but there is no proof that they really exist

Answer 9

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

Merely having a very large mass is not enough to make a black hole - if it were, most galaxies would be black holes. A black hole consists of mass concentrated into an abnormally small volume.

Black holes can be divided into several size categories:

Supermassive black holes containing millions to billions of solar masses are believed to exist in the center of most galaxies, including our own Milky Way.

Intermediate-mass black holes, whose size is measured in thousands of solar masses. Intermediate-mass black holes have been proposed as a possible power source for ultra-luminous X ray sources.

Stellar-mass black holes have masses ranging from 1.44 to 15 solar masses. This is narrower than the range of masses found in "normal" stars because of the way in which black holes are formed: the smallest star which is large enough to produce a black hole will form a black hole of 1.44 solar masses (the Chandrasekhar limit); large stars usually blow away a significant percentage of their mass in supernovae as part of the process that forms black holes.

Small black holes which are smaller than stellar-mass black holes but larger than micro black holes.

Micro black holes, which have masses similar to that of a helium atom.

Answer 10

It is nothing but a star which is collapsed inward and sucks all the the light and objects present near it & goes on expanding.
There are chances for the sun to become a "black hole".