What Are Black Holes ?

Among all the things that consist the Universe, perhaps Black Holes are one of the most fascinating things.

A black hole is nothing but a region in space where the pulling force of gravity is so strong that nothing, even electromagnetic radiation like light is able to escape. As matter has been pressed into a tiny space a very strong gravity occurs. This compression takes place at the end of a star's life. Majority of black holes which are found in the universe are a result of dying stars.

Black holes are invisible because no light can escape its very high gravitational pull. However, as light itself bends near a black hole we get lensing of light surrounding the black hole. Certain space telescopes with special instruments can help find black holes. They are able to observe the behaviour of material and stars that are very close to black holes.

The outer layer of the black holes is called its event horizon. Anything approaching the black hole approaches its event horizon. Mathematically it takes about an infinite amount of time to cross the event horizon of a black hole. The core of the black holes is known as the Singularity. It is known as Singularity because highly dense mass is concentrated at a single point. Any Object approaching the black hole can never escape from it as near its event horizon the escape velocity required is more than the speed of light. Black holes reduce mass gradually due to Hawking Radiation. But it occurs at an unimaginably slow rate. From the information conservation principle, no information existing in this Universe can be destroyed. Then black holes literally destroys information as anything entering the black holes can never return back. Again it may be possible that the information of any object entering the black hole does not get eliminated rather it is converted from one form to another and later that information gets released from it due to Hawking radiation.

Although the formation of a black hole is understood, one perpetual mystery in the science of black holes is that they appear to exist on two radically different size scales. On the one end, there are the countless black holes that are the remnants of massive stars. Spread across throughout the Universe, these "stellar mass" black holes are generally 10 to 24 times as massive as the Sun. A black hole can be discovered by astronauts when a massive star comes in near proximity of a black hole and as a result of its high gravitational forces, disfiguration of matter takes place around it. Most stellar black holes are impossible to detect. Scientists made an estimation that there are as many as ten million to a billion such black holes in the Milky Way alone.

On the other end of the size chart are the giants known as "supermassive" black holes, which are millions, if not billions, of times as massive as the Sun. Astronomers believe that supermassive black holes lie at the centre of all large galaxies, even our own Milky Way.

A black hole has only three independent physical properties: mass, charge, and angular momentum; and apart from these three, the black hole is featureless. If the conjecture is true then, any two black holes that share the same values for these properties, or parameters, are indistinguishable from one another.

If our planet Earth is put before a black hole which is of the same size of Earth then the tidal forces of the black hole would rip apart Earth until it finally disappears in the hole.