A supernova core made of more than about 3 times the mass of sun .it doesnt stop collapsing at the neutron stage.(it is a stage where a supernova leaves behind a small star that emits beams called pulsar)it collapses until it becomes denser and smaller and finally black hole.the centre of the black hole is called singularity and the boundary event horizon . the five types of black holes r Schwarzschild , middle - weight , kerr , reissner nordstrom and super massive black holes.its gravitation is so strong that even light or other forms of radiation cannot escape from it . THE BLACK HOLE CANNOT BE detected directly , but is identified by the effect it has on objects around it . it can be also detected by x ray telescopes such as the indian satellite CHANDRA X RAY OBSERVATORY THAT IS ONE OF THE BEST X RAY TELESCOPES .