A Black hole is an object in space which is invisible. Why? Because even light cannot come out of it because of the gravitational pull of the object. In fact, nothing can come out of it because of its strong gravity.
How are Black holes are formed? In the 18th century John Mitchel ideated the concept of Black hole. Interestingly, Sir Isaac Newton’s Theory of Gravitation cannot explain Black hole; Albert Einstein‘s General theory of Relativity can. According to Relativity can explsain that a massive body, collapsed, can form a compact mass that it can distort space and time around it. The boundary from where nothing returns is called Event horizon. It is not easily possible to detect a Black hole as it has no detectable features locally. It is like a black object.
After General theory of Relativity was published in 1915, Karl Schwarzschild in 1916 was the first to find the solution of Black hole . The characterizations of Black hole could be amply explained. It should be noted that Black hole cannot be explained by Newton’s theory of Gravitation. Black holes were a subject of curiosity from a long time. Generally it was characterized by “the region in space” from which nothing can escape, not even light. In 1960s theory showed the possibility of Black hole. The first Black hole was discovered in 1971 and named as Cygnus X-1. Astrophyscists have discovered several Black holes. Black holes can be identified by the interaction between them and their neighbours. Stars passing by will be swallowed. If some stars orbit Black holes their orbit can give the size and mass of the black hole. These discoveries can show what is what and give the safe view of Solar system. Presently many Black holes have been discovered and it has been seen that there isa huge Black hole in the Milky way, the size being 4.3 million solar masses.