The Universe is very big place but we can only see a certain parts of it it contains the Pegasus cluster, Virgo cluster, local group (we live in the local group), Centaurs cluster, Fornax cluster, Hydra cluster.
Cluaters are massive groups of galaxies bucked to gather it may contain anything to a few dozen to few thousand. That might sound a lot but it mostly believed to be made of darkmatter.

A black hole is an extremely dense celestial body which is believed to exist in our universe. THe gravitational force of a Black Hole is so strong that light can enter it but not escape.

The Black Hole Concept was developed by a German Astronomer in 1916, named Karl Schwarzschild. He based his studies on Albert Einstein's general theory of gravity.

The point when no matter can escape the gravitational force of a black hole is called the Event Horizon. You can only see a black hole when light is entering it, not any other time.

Black Holes are still a mystery to mankind which is why we don't know all the facts about Black Holes.

Black Holes are also called Neutron Stars.