Black Hole – A black hole is an object with a stong gravitational field in which the light cannot pass through from its surface. A black hole may be formed when a massive object (very big object ) undergoes uncontrolled contraction (collapse) because of the inward pull of ots own gravity.

Description of formation of black hole – When a supernova explosion of a very massive star occur then the gaseous matter present in the outer shell (or envelope) of the star is spread into space but the core of the star survives during supernova explosion. This heavy core of the supernova star continues to contract (shrink) and becomes a neutron star. The fate of this neutron star depends on its mass. If the neutron star is very heavy, then due to massive gravitational attraction, it would continue to contract for an indefinite period (or continue to shrink in size indefinitely). The vast amount of matter present in a neutron star would be ultimately packed into a mere point object. Such an indefinitely dense object is called a black hole.

Thus, black holes are created by the indefinite contraction of heavy neutron stars under the action of their own strong gravity. The neutron star shrink so much and become so dense that the resulting black holes do not allow anything to escape, not even light from their surface. This is because the black holes have tremendous gravitational force. Since even light cannot escape from black holes, therefore black holes are invisible, they cannot seen. The presence of a black hole can be felt only by the effect of its gravitational field on its neighboring object in the sky.