What is a black hole
Black holes are, for many people, the most fascinating thing in the universe. Imagine the mass of the Earth in the size of a basketball ball. Now imagine a black hole with the size of Earth, its mass could be thousands times the mass of our sun. Black holes are very dense objects and the result is a very strong gravitational field that nothing can escape from it, not even light. The existence of black holes was known centuries ago but the term was created by John Wheeler on 1967.
How a black hole is created
Stars like humans and everything else die. When a huge star dies (supernova explosion) it does not disappear completely but a dense core remains. If the mass of that remaining core is at least three times more than the mass of our sun, gravity is the winner force, star collapses and a black hole is born. There are billions black holes in the universe and it is believed that they can be divided into two categories. “Stellar mass” black holes which are 10-25 as massive as the Sun and “Supermassive” black holes which are millions of times as massive as the sun. If the small ones have so strong gravitational field, then I can only imagine how strong is the gravitational field of the big ones, which are millions of times as massive as the small ones.
How scientists study black holes
We said that a black hole have a great gravitational field that not even light can escape from it. So, how is possible for scientists to observe those things? They can’t directly but they can see how other masses near a black hole behave. Black hole can pull a star or even a galaxy towards itself and destroy it. The star or any matter which is pulled by a black hole accelerated and heats up which cause the emission or x-rays. The effects that a black hole has to its neighbours are dramatic and gamma rays are emitting because of that. Scientists can observe and study the movement of nearby stars and the emission of x-rays and gamma rays.
A very informative and cool flash animation explaining black holes can be found at Think Technologies.