For three years now, NASA has been marking Black Hole Friday on November 27 and what that means is we get to see some more of these collapsed stars that exist in our universe.

What is a black hole?

When the force of gravity is strong enough to trap light and other matters, a black hole is formed in space. This usually happens when a star in dying, says NASA .

Since all light around it is trapped, people are unable to see black holes. One can only see black holes through space telescopes and special tools.

So here are some pictures of what the black holes in our universe look like:

An artist's drawing a black hole named Cygnus X-1. It was formed when a large star caved in. This black hole pulls matter from blue star beside it.

An artist's drawing shows the current view of the Milky Way galaxy. Scientific evidence shows that in the middle of the Milky Way is a supermassive black hole.

This image of the centre of the Milky Way galaxy was taken by the Chandra X-ray Observatory.

Sagittarius A* is the black hole at the center of the Milky Way galaxy.

( All images and information have been taken from the NASA website )