what is a black hole?
607184
A black hole is the thing that happens when a star, like our Sun burns off it's helium resources and it explodes. This reverses the gravitational pull and sucks everything towards it, even light.
63870
Not much is known about black holes. What is known is only an estimate of how it might work.
32519
A Yahoo Search for black holes turns up a bunch of useful sites:\n\nhttp://search.yahoo.com/search?p=black+holes&y=Search+the+Web&ei=UTF-8&fr=sbc-web&x=wrt\n\nThe Wikipedia article is a good start:\n\nhttp://en.wikipedia.org/wiki/Black_hole\n\nAnother really good starting place is Stephen Hawking's new book "A Briefer History of Time".  Which is an update to his previous book "A Brief History of Time"\n\nhttp://shopping.yahoo.com/search?fr=ytff1-&p=A+briefer+history+of+time&ei=UTF-8&cop=mss
849237
There's most likely not an 'other side'.  A black hole is a bunch of matter that's been compressed down into a singularity, or an extremely dense spot.  More stuff falling into the hole isn't going anywhere; it's just contributing to the density of the black hole itself.
211187
they become black holes
1138674
A star is stationary object and a black hole is a result of dying star. Black holes are stationary objects.\nThey posses a great gravitational force. It is so great that it can even suck in light.\nDue to such gravitational force it makes objects near it to revolve around it with tremendous speed.\n\nThe closest black hole to earth lies just 1,600 light-years \n(1 light year = 9.4605284 × 10^15 meters ) from Earth on the way to the centre of the Milky Way in the direction of the constellation Sagittarius.\n\nBut if you want to test the above facts and experience it yourself then just wait till sun becomes one black hole!!!! (after around 5-6 billion years)  (Sun can also become neutron star or nebula so may be you cannot experience it!!)
893247
A "black hole" means that an object the size of a large star (larger than our sun) has burned up its atomic fuel so that it can no longer support the weight of its own matter and therefore collapes on itself.  This collapse of the star's own matter is so powerful that it crushes that matter (the atoms of the matter are crushed which means the electrons of those atoms are driven into the atom's nucleus, the protons and neutrons of the nucleus are crushed and even the quarks that make up the protons and neutrons are crushed) down to a point like place which is called a 'singularity'.  However, the gravitational force that that matter had associated with it still exists surrounding the singularity.  That gravitational force is so strong that nothing, not even light, can escape, hence the name 'black hole'.
23482
In astronomy, an object so massive that nothing, not even light, can escape its gravitation. Black holes were given their name because they absorb all the light that falls on them. The existence of black holes was first predicted by the general theory of relativity. Supermassive black holes have been found in the centers of many galaxies. Stellar black holes are thought to arise from the death of very massive stars. Astronomers expect to find many stellar black holes in the Milky Way. \n\n\nFiguratively, the term black hole is used to refer to a total disappearance: “They never saw the man again — he might as well have fallen into a black hole.”
794668
Well, black holes are mysterious simply because they are regions where light itself cannot escape!  If you go by general relativity black holes are singularities where space and time lose their meaning in the rational sense!  As for black holes leading to some location, most likely that is not the case.  Such an object is a wormhole, which is a theoretical solution to Einstein's field equations like black holes are.  But, wormholes have not been observed in nature and they are unstable to the point where if even a tiny amount of mass enters the wormhole it will collapse it and destroy the matter before it ever gets to the other side!  So, that being true a black hole has no opening somewhere else, because if it did it would collapse the same way.  However, Stephen Hawking showed that black holes do dissipate over many billions of years because of quantum tunneling.  Turns out some matter/energy actually gets out of the black hole!  So, we still have alot to learn about the nature of black holes, because we still have to learn alot about gravity!
1952
A black hole is formed by a star, most likely a neutron star, collapsing into a space a few kilometers across. It is made up of the same thing a neutron star is, mainly hydrogen, helium, oxygen, and a few other elements. Once the black hole forms, it can absorb large amounts of matter from surrounding stars.
209721
Black holes are a theory, we suspect that some anomalies in space are black holes. White holes are desired by our nature to balance the negative energy of black holes. However the Begy concept of gravity as an external force acting on our universe more than compensates for the negative E of black holes and even predicts a source of energy that is constantly flowing into the universe which can only be detected as the force of gravity. According to the Begy theory, black holes would be anchors in time and space where the gravitational force is neutralized.
38830
a black hole is a point of infinite density and gravitational pull. First of all you would be dead from different gravitational pulls from the black hole. Second of all, time from your perspective would stop, assuming that einstein is correct and your image would be spread out over an infinite period of time so your friend would see nothing.
128460
It might be, or it might be a neutron star. We do not really know. \n\nThere are some other objects in the sky which are much more certainly black holes, from their masses and other properties.
661081
A black hole is a concentration of mass great enough that the force of gravity prevents anything past its event horizon from escaping it except through quantum tunnelling behaviour (known as Hawking Radiation). The gravitational field is so strong that the escape velocity past its event horizon exceeds the speed of light. This implies that nothing, not even light, inside the event horizon can escape its gravity. It is, however, theorized that wormholes can provide an exit path for energy or matter. The term "black hole" is widespread, even though it does not refer to a hole in the usual sense, but rather a region of space from which nothing can return.
17
The current scientific theory holds that black holes are formed when stars of sufficient mass (about 3x the mass of our Sun) reach the end of their life and collapse down into a singularity, which is, in essence, an infinitely small point with a huge amount of gravity - gravity so powerful that not even light can escape it's pull if it gets too close. It is also thought that black holes can be formed from smaller masses if external energy/pressure is exerted to squeeze the mass into a singularity.\nNot sure if there's any direct experimental evidence of creation, but there is evidence that they exist. Cosmologists use several different methods to detect blacks holes, such as by looking for light being bent and/or disappearing as it travels from remote stars towards us, and also by looking for bursts of x-rays that are given off as matter is sucked into the back hole and destroyed.\nFun fact: current evidence and theory suggests that the center of the Milky Way is a giant black hole that was formed as the densly packed stars in the center collapsed and sucked each other in.
651133
The black hole is where the force of gravity has successfully joined our known universe back with infinitely dimensional space. \n\nSpace is where our universe was born in a disturbance known as the big bang.  \n\nThe black hole is the grand finale to gravity, gravity's 'goal' creating a porthole to where we came from before the big bang.  \n\nGravity is the connection space has with our universe, too stubborn to let us go and will one day bring us back to become nothing and everything with it once again.\n\nPeace Out
127702
Black holes are full of electrons.They are not capable of any expansion or constriction. Time also does not expand.