Black Hole

If the core of exploded star has a mass of more than three Suns, then even a neutron star is not the end for it. Instead, its become something more bizarre: a black hole. No force can shore up a dead star weighing more than tree solar masses against the inward pull of its own gravity. It continues to shrink, becoming ever smaller and denser until its gravity becomes so great that nothing can escape form it, not even its own light. It has dug its own grave- a back hole,
Since a black hole is by definition invisible, it is of only academic interest to amateur observers. However, professional astronomers have detected X-ray emissions from various source which they believe are caused by hot gas plunging into the bottomless pits of black holes. The best-know candidate for a black hole, Cygnus X-1, orbits a 9th-magnitude star in the neck of Cygnus, the Swan.