mystery of the black holes 

  

Imagine a star made of matter dense enough to go into a matchbox which weighs 10,000million tons. If a rocket is to escape from earth's gravity, it needs to attain a speed of about 25,000 mph; but the gravity of this star would be so enormous that there would be no escaping from it even at 669,6000,000 mph-the speed of light. Indeed light itself  would not be able to escape, making the star forever invisible. Such stars are  believed to exist in the universe as light cannot leave them. No one has over seen one; but astronomers have good reasons to assume that they are there. These are called black holes. black holes to make = n+si+h, it all element create gravity.