Black Hole

   Black hole is a thing which attract everything of the universe which is nearest to it and engulf the thing inside it.

   

    If we throw a thing upside then it will come back to the downward, this happens due to the gravitational force of the earth. If we have to throw the thing out of the gravitational pool of the earth than we have to give some energy and velocity to the thing, suppose we are standing in an open field and we threw the thing with some energy and velocity through which the thing can go out of the earth's gravitational pool and that velocity is called escape velocity.

   

   Now the question arises ,i.e., Whom does the  escape velocity depends on?

ANS- Escape velocity depends upon the mass of the earth and size of the  earth.

   And we know that moon is smaller than earth on behalf of size, so the escape velocity of moon is lesser than earth that is why there is no atmosphere because the gases of moon get heat and escape from the atmosphere of the moon.

  

  Let us suppose  we take an atom and put the mass of a mountain in the atom. Now the mass of the mountain came into the atom, if any light want to go out of the the atom then it have to break the escape velocity of the atom, but it can't beak the escape velocity of atom because an atom which can engulf a mass of a mountain which is billion and trillion times larger than an atom, than the escape velocity of that atom will greater than the velocity of the light. Black hole is is just like that, if we suppose a star which is 1 crore times larger than our sun, so the escape velocity of that star will such strong that it will not allow anything around it to escape from that atmosphere or from that escape velocity and engulf everything. In simple words it is not a hole in the universe. There is something in the universe which is physically present there bur we are totally depend on our vision and depends on the reflection of that object that falls on eyes or our equipment, so we are not able to see the black hole. But there is a circle around the black hole, you can see in the picture below, but these are the imagination of an artist.

                                                                                                                                  

   There is a black hole which is present in billions of light year away from us, that is in M87.

      

  When black hole engulf something it generates some light around the circle and it is the light of the objects that it engulf in. And black hole can move light around it.