what is black hole.define?

Question

What is a black hole?Why it is named so.When it was first discovered and by whom?How does it work?Does it has any impact in our life now or near future?

Answer 1

Definition:

A Black Hole is, in essence, the corpse of what once was a star. When a star with at least five times the mass of our Sun runs out of fuel, it implodes. It's own gravity presses it together -- and presses it together some more, until there's nothing really left. What you have then is a Black Hole: a tiny speck of matter (well, matter isn't the right word, really), but with immense mass.

Origin:

The very first mention of the concept was about two centuries ago. It was an English geologist, John Michell, who realized that it would be theoretically possible for gravity to be so overwhelmingly strong that nothing -- not even light traveling at 186,000 miles an hour -- could escape. To generate such gravity, an object would have to be very massive and unimaginably dense. At the time, the necessary conditions for "dark stars" (as Michell called them) seemed physically impossible. And due to lack of evidence the idea was soon dropped.

In 1916, the concept was revived when German astrophysicist Karl Schwarzschild decided to compute the gravitational fields of stars using Einstein's new field equation. Schwarzschild limited the complexity of the problem by assuming the star was perfectly spherical, gravitationally collapsed, and did not rotate. His calculations yielded a solution aptly called a Schwarzschild singularity. Scientists theorize that this singularity lies in the center of these dark stars.

The term 'Black Hole':

The new term that was used since then to describe it was "Gravitationally Collapsed Star" until 1969, when John Wheeler coined the term "Black Hole" for the first time.

First Discovery:

Although the theory & the term goes back quite a few decades, the first actual scientific evidence was found only in 2000 when a newly spotted object was first noticed as an X-Ray source. The new observations were made using a new 6.5-meter (255-inch) telescope at the MMT Observatory on Mount Hopkins in Arizona.

The newly found black hole is estimated to be six to eight times as massive as our Sun, larger than some but smaller than many. It lies approximately 6,000 light-years away, 62 degrees above the galactic plane. It was spotted because of the motion it imparts on a nearby normal star, one smaller than our Sun, which orbits it every 4.1 hours.

Astronomers have previously identified 10 similar objects in the galactic plane, and an additional 20 X-ray sources in the Milky Way are suspected of being black holes. But they are all suspicions, except this new discovery that is more promising.

Also, though they may have some evidence now, we are yet to actually SEE a 'Black Hole', which is impossible so far, 'cause even light is known to not escape it. The matter falling into the black hole, while it can't be seen, is heated to millions of degrees by friction and gravity, and the heat energy produces strong X-ray emissions. Of these X-Ray emissions, some that do slip by the 'event horizon' (point around the black hole from where nothing escapes), can be detected & point towards a Black Hole.

How does it work?:

To keep it simple, a space shuttle, for example, needs to accelerate beyond the 'escape velocity' of our planet to escape our atmosphere into the orbit. If its velocity is lesser than the 'escape velocity' of our planet, it can never get out into space.

Similarly, in case of a black hole, this escape velocity is way too high (even higher than the velocity of light which is 186, 200, 000 miles per second) because of the immense gravity. Due to this, its impossible, even for light, to escape its gravity & it gets sucked in it, apart from everything else.

How it impacts matter is still a theory & we don't know for sure, but it is believed that everything is turned into a thread of almost zero width & is passed through a hole which is no bigger than the eye of a needle.

It's impact on our life:

None, whatsoever in the known times. Before one gets even close to us, chances are that we would be extinct.

PS: Just some additional info, the closest 'black hole', although without any evidence so far, is believed to be at the core of our milky way & supposedly has a mass of 2.6 million suns.

Answer 2

A black hole is defined by the escape velocity that would have to be attained to escape from the gravitational pull exerted upon an object. For example, the escape velocity of earth is equal to 11 km/s. Anything that wants to escape earth's gravitational pull must go at least 11 km/s, no matter what the thing is — a rocket ship or a baseball. The escape velocity of an object depends on how compact it is; that is, the ratio of its mass to radius. A black hole is an object so compact that, within a certain distance of it, even the speed of light is not fast enough to escape.

Using Newton's Laws in the late 1790s, John Michell of England and Pierre LaPlace of France independently suggested the existence of an "invisible star." Michell and LaPlace calculated the mass and size — which is now called the "event horizon" — that an object needs in order to have an escape velocity greater than the speed of light. In 1967 John Wheeler, an American theoretical physicist, applied the term "black hole" to these collapsed objects.
A black hole itself is invisible because no light can escape from it. In fact, when black holes were first hypothesized they were called "invisible stars." If black holes are invisible, how do we know they exist? This is exactly why it is so difficult to find a black hole in space! However, a black hole can be found indirectly by observing its effect on the stars and gas close to it. For example, consider a double-star system in which the stars are very close. If one of the stars explodes as a supernova and creates a black hole, gas and dust from the companion star might be pulled toward the black hole if the companion wanders too close. In that case, the gas and dust are pulled toward the black hole and begin to orbit around the event horizon and then orbit the black hole. The gas becomes heavily compressed and the friction that develops among the atoms converts the kinetic energy of the gas and dust into heat, and x-rays are emitted. Using the radiation coming from the orbiting material, scientists can measure its heat and speed. From the motion and heat of the circulating matter, we can infer the presence of a black hole. The hot matter swirling near the event horizon of a black hole is called an accretion disk.


Black holes have little effect on the Earth. The closest black holes are
many light-years away, and typical black holes are only a few miles
across. If a black hole were to hit the Earth, however, the effects would
be disasterous, with the entire planet being ripped to shreds in a matter
of seconds. Luckily this is extremely unlikely and will almost certainly
never happen.

Answer 3

A black hole is a celestial object of such extremely intense gravity that it attracts everything near it and prevents everything, including light, from escaping. The term was first used in reference to a star in the last phases of gravitational collapse.

Gravitational collapse begins when a star has depleted its steady sources of nuclear energy and can no longer produce the expansive force, a result of normal gas pressure, that supports the star against the compressive force of its own gravitation. In some cases, nothing remains to prevent the star from collapsing without limit to an indefinitely small size and infinitely large density, to create a black hole.

At this point the effects of Einstein's general theory of relativity become paramount. According to this theory, space becomes curved in the vicinity of matter (this is the meaning of gravity); the greater the concentration of matter, the greater the curvature (the greater the gravity). When the star shrinks below a certain size determined by its mass, the extreme curvature of space seals off contact with the outside world. The place beyond which no radiation can escape even not light.

It is now believed that the origin of some black holes is no stellar. Some astrophysicists suggest that immense volumes of interstellar matter can collect and collapse into super massive black holes, such as are found at the center of some galaxies.

Because light and other forms of energy and matter are permanently trapped inside a black hole, it can never be observed directly. However, a black hole could be detected by the effect of its gravitational field on nearby objects (e.g., if it is orbited by a visible star), during the collapse while it was forming, or by the X rays and radio frequency signals emitted by rapidly swirling matter being pulled into the black hole. A small number of possible black holes have been detected, although none of the discoveries has been conclusive.

Answer 4

A black hole is a concentration of mass whose gravitational field is so strong that nothing can escape. As an object moves closer to a black hole, the energy required for it to escape continues to increase until it becomes infinite at the event horizon, the surface beyond which escape is impossible. Inside the event horizon, the geometry of spacetime is distorted in a way that makes moving closer to the central singularity inevitable no matter how the infalling object moves.

Answer 5

At the end of a star's life, it becomes what is known as a Red Giant. The star expands thousands of times in size. As the star's remaining fuel burns off, the center of the star becomes more concentrated, increasing its gravitational effect on the surface of the star. Eventually this gravitational pull from the center of the star becomes so great, it pulls the entire surface of the star in upon itself, causing a violent colapse and the release of massive amounts of energy.

After this release of energy, the star ends its life burning off its remaining solar fuel as a White Dwarf... most of the time. Every once in a while, there is an exceptionally huge star. When one of these becomes a Red Giant, it is an amazingly huge Red Giant. As it finally collapses in upon itself, instead of becoming a White Dwarf, the extreme gravitational forces cause it to continue collapsing beyond the White Dwarf stage. All its matter continues to compress until it is so dense that just one teaspoon of this material weighs more than our Earth.

That explains what it is and in a very general sense, how it works... at least when you consider that the "work" it does is simply to act as a point in the Universe of extreme gravitational attraction. Fortunately for us, black holes have no impact on our lives now, nor will they have any effect on us in the near future because they are all too far away from us. If our solar sysem would happen to drift past one, our sun and all its planets, including Earth, would be pulled onto the surface of the black hole and crushed into tiny teaspoon-size clumps. All life would cease to exist.

But, as I mentioned earlier, that won't happen. We would first have to get close enough to one to be drawn into its gravitational field, also known as the Event Horizon, and we just don't happen to be travelling in the direction of any.

Its interesting you would ask who first discovered black holes, since there are still scientists who argue they don't exist, and if they don't exist, they can't be discovered. However, English geologist John Mitchell is generally given credit as the first person to propose the idea that they might exist in a paper to the Royal Society in 1784.

Since Mitchell's paper, several scientists and mathmeticians have offered evidence to support the existance of black holes including French mathmetician Pierre-Simon Leplace in 1796 and later, in 1915, Albert Einstein, who showed that light can be effected by gravity, which is partially how a black hole gets its name... the gravitational pull of a black hole is so great that not even light can escape it. And there you have it.

Answer 6

Hi,

A black hole occurs a certain star dies but instead of the normal effect the start creates a black hole.

The black hole might be a tunnel to other parts of the space or other universes. It benefits us if we can travel through it ... less time to travel.

Nothing can escape from this whole not even light itself...

Karl
http://www.furl.net/furled.jsp?topic=ds

Answer 7

A black hole is a region of space that has so much mass concentrated in it that there is no way for a nearby object to escape its gravitational pull. Even light gets pulled by its gravitational force and hence these are not visible to us. Only by way of other objects nearer to the black hole behave scientists estimate the location of black hole.

Answer 8

A black hole is the final stage of the star. It attracts each and every object which comes near to it. I don't know who discovered it and when it was discovered. Black dwarf/hole doesnot shine and it has his attracting power which attracts every celestial object which comes near it.

Answer 9

A singularity.

Answer 10

blackhole.com was made by some pervert who probably makes millions off of it now! DAMN!