So, what is a black hole ?

TL;DR: It's a huge dying star.

There are a lot of stars in our universe and some of them are about to die. When a star is at the end of its life, it starts to burn all its remaining power in order to grow very fat or to become very little as a white dwarf. But if the star is big enough, it will absorb its own energy and litterally collapse on itself, forming an object so dense that if it were a car it would have the same weight as Earth (the planet).

Why is a black hole black ? Simply because this object is so dense it absorbs anything, even light particles. Every object produces or reflects light. Here we have something that keeps light from getting out therefore we cannot see what it looks like. If you try to get close to it, light and other things will be distorded and stretched.

You can look for more at Wikipedia[en.wikipedia.org] or in this VSauce video. http://www.youtube.com/watch?v=3pAnRKD4raY.

So first, you need to create a system or import an existing one.

• set pause on the top-left of the screen
  
• select an object
  
• change its diameter at the right of the screen by clicking on the value

• select "Black Hole"
  
• confirm the new mass of the object
  
• un-pause
  
• enjoy !