What are black holes.

                                  At first the concept of black hole was given by Albert Einstein.

                            Black holes are the stars which had removed and had more gravity than thier mass. So that there mass is gone inside them and start contracting and a stage reaches when they transform into a black hole. It 25% chances for a star to be a black hole.

                            A black hole in space attracts every thing towards it and start contracting.A stage reaches when it is gone. A black hole finishes as it is small but if it gets mass ,it starts growing.A black hole has alot of gravity that it can swallow more big stars than itself.even light canot escape from it.