What is a galactic Black Hole?
A very compact and energetic microwave source exists at the centre of the Milky Way Galaxy. There is a theory that this is caused by a giant Black Hole or galactic Black Hole having a mass of 100 million stars. There is also another theory that there are such galactic Black Holes at the centre of every galaxy. For example, the galaxy NGC-6240 which is 300 million light years away from earth is suspected to contain a black hole 100 billion times as massive as the Sun.
To what extent will matter in a Black Hole collapse?
Matter in a black Hole will continue to collapse indefinitely until, in principle, it is compressed into appoint of infinite density Known as a singularity (or Schwarzchild singularity).
What is a gravitational lens?
Light rays passing near a black Hole would be sent toward the Black hole due to the tremendous gravity exerted by the Black Hole in the same way as a lens makes light rays converge. The Black Hole therefore behaves as a gravitational lens deflecting the light rays.