A black hole is an invisible object or a region of space in the universe that has such a strong gravitational force that nothing can escape it. Many astronomers believe that there are millions of black holes in the universe. They are invisible because of the fact that they trap anything, even the fastest thing there is – light. The gravity in a black hole is extremely powerful that it can compress tremendous amounts of matter into an unbelievably tiny space. If the earth will be caught by a black hole, it will be packed into a space as small as a marble.

Their formation is believed to start when an enormous body such as a star runs out of nuclear or internal fuel. This decreases its internal pressure, which eventually causes it to have weak resistance to its own gravitational force. When this reaction is not stopped, it then collapses under its own pressure into a black hole. A gigantic explosion happens where the star throws off its outer layers and its core collapses. This occurrence is called ‘gravitational collapse’ and is the reason for the formation of most stellar mass black holes. However, very few stars become black holes when they die. Most massive stars disintegrate to become neutron stars. Neutron stars are dense stars made up mostly of neutrons.

Anything that strays past the event horizon of a black hole will have uncontrollable direction. Its path will inevitably be aimed towards the black hole and there is no escape whatsoever. Researchers found that captured matter inside the black hole is not kept forever, but deteriorates due to the thermal energy that the black hole emits.

John Michell was the first to propose the possibility of the existence of an object with a gravitational force so strong that it can capture anything including light in 1783. He is an amateur British astronomer.

Albert Einstein’s theory of gravitation, also known as ‘general relativity’ best describes how a black hole is created. It predicts that a black hole formed by the collapse of a star is about 100,000 times bigger than the sun and almost featureless. It reasons that nothing escapes a black hole’s interior due to its ability to warp the path and space-time in which the object travels.

In space, a black hole, although almost undistinguishable, can be detected through a few techniques. X-ray and gamma rays can be emitted from a spacecraft to determine where a black hole could be present. The exact location may then be learned by a method called ‘gravitational lensing’. A band of light is emitted and expected to bend if it will pass through an object with strong gravitational force. A black hole’s force will warp the space-time of the section of light that passes it and makes its existence known.

Studies have shown that every ‘active galaxy’ has an extremely huge black hole in its center. An active galaxy is a galaxy found to have bizarre characteristics. It has a compact region in its center that has much higher brightness over all possible electromagnetic frequencies. These central black
holes may be millions or billions of times larger than the sun.

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