Black holes

A black hole is a gravitationally collapsed object that is formed when the mass of an object is increased while it's size remains fixed, or when the size of an object is reduced while it's mass is kept constant. Black holes were initially predicted before there were any observational data to support there existence, but it has now become an experimental fact that they exist in our universe. The presence of a supermassive black hole at the center of our galaxy has been established convincingly. Most likely, there are millions of black holes in every galaxy. They are the remnants of ordinary stars that were a few time mire massive than the sun.