BLACK HOLE

BLACK HOLE 

are out there .........

But , What are they ?

The Mass of the Earth Creates The Gravity that Pulls things to the ground  with enough power.
we can escape the gravity and the leave the earth behind. But if you could take the Earth and squeeze it to the size of marble the gravity of the surface would be much greater not even a beam of light could escape We call this is a BLACK HOLE. Fortunately neither the Earth nor the Sun will ever become a Black Hole. But, Black holes do the exist........ Black holes Gravity's Relentless pull.

The nearest black hole is many lightyears away from the Earth,  Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, super massive black holes of millions of solar masses may form. There is general consensus that super massive black holes exist in the centers of most Galaxies.

The name "black hole" was introduced by John Archibald Wheeler in 1967. It stuck, and has even become a common term for any type of mysterious bottomless pit. Physicists and mathematicians have found that space and time near black holes have many unusual properties. Because of this, black holes have become a favorite topic for science fiction writers. However, black holes are not fiction. They form whenever massive but otherwise normal stars die. We cannot see black holes, but we can detect material falling into black holes and being attracted by black holes. In this way, astronomers have identified and measured the mass of many black holes in the Universe through careful observations of the sky. We now know that our Universe is quite literally filled with billions of black holes.

n 1687, Isaac Newton showed that all objects in the Universe attract each other through gravity. Gravity is actually one of the weakest forces known to physics. In our daily life, other forces from electricity, magnetism, or pressure often exert a stronger influence. However, gravity shapes our Universe because it makes itself felt over large distances. For example, Newton showed that his laws of gravity can explain the observed motions of the moons and planets in the Solar System.

Albert Einstein refined our knowledge of gravity through his theory of general relativity. He first showed, based on the fact that light moves at a fixed speed (671 million miles per hour), that space and time must be connected. Then in 1915, he showed that massive objects distort the four-dimensional space-time continuum, and that it is this distortion that we perceive as gravity. Einstein's predictions have now been tested and verified through many different experiments. For relatively weak gravitational fields, such as those here on Earth, the predictions of Einstein's and Newton's theories are nearly identical. But for very strong gravitational fields, such as those encountered near black holes, Einstein's theory predicts many fascinating new phenomena.

All matter in a black hole is squeezed into a region of infinitely small volume, called the central singularity. The event horizon is an imaginary sphere that measures how close to the singularity you can safely get. Once you have passed the event horizon, it becomes impossible to escape: you will be drawn in by the black hole's gravitational pull and squashed into the singularity.

The size of the event horizon (called the Schwarzschild radius, after the German physicist who discovered it while fighting in the first World War) is proportional to the mass of the black hole. Astronomers have found black holes with event horizons ranging from 6 miles to the size of our solar system. But in principle, black holes can exist with even smaller or larger horizons. By comparison, the Schwarzschild radius of the Earth is about the size of a marble. This is how much you would have to compress the Earth to turn it into a black hole. A black hole doesn't have to be very massive, but it does need to be very compact!

Some black holes spin around an axis, and their situation is more complicated. The surrounding space is then dragged around, creating a cosmic whirlpool. The singularity is an infinitely thin ring instead of a point. The event horizon is composed of two, instead of one, imaginary spheres. And there is a region called the ergosphere, bounded by the static limit, where you are forced to rotate in the same sense as the black hole although you can still escape.

What is inside a black hole?

We cannot glimpse what lies inside the event horizon of a black hole because light or material from there can never reach us. Even if we could send an explorer into the black hole, she could never communicate back to us.

Current theories predict that all the matter in a black hole is piled up in a single point at the center, but we do not understand how this central singularity works. To properly understand the black hole center requires a fusion of the theory of gravity with the theory that describes the behavior of matter on the smallest scales, called quantum mechanics. This unifying theory has already been given a name, quantum gravity, but how it works is still unknown. This is one of the most important unsolved problems in physics. Studies of black holes may one day provide the key to unlock this mystery.

Einstein's theory of general relativity allows unusual characteristics for black holes. For example, the central singularity might form a bridge to another Universe. This is similar to a so-called wormhole (a mysterious solution of Einstein's equations that has no event horizon). Bridges and wormholes might allow travel to other Universes or even time travel. But without observational and experimental data, this is mostly speculation. We do not know whether bridges or wormholes exist in the Universe, or could even have formed in principle. By contrast, black holes have been observed to exist and we understand how they form.