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You may have had that these things called
black holes
The dark lurking creatures in space,
the characters in science fiction
but what exactly are they?
A black hole is a  region spacetime,
that is so dense, that not even light can escape it's gravity.
the definition of a black hole is a place
where the escape velocity is faster than the 
speed of light.
but what does this mean?
escape velocity is all to do with gravity
if an object has mass, it has gravity.
skyscrapers, cars, trees, you and me,
we all have gravity. 
But objects need to be really big before you can feel the effects of gravity. 
like the size of a planet.
The earth has a huge mass an it's gravity stops everything on it from floating off into space. 
Gravity is strongest near the surface,
getting weaker, and weaker, the further away you get from an object. 
the escape velocity is the speed you need to 
travel from an object 
so that  gravity no longer has a hold on you.
For earth, this is about 7 miles per a second
for black hole it's faster than the speed of light. 
that's faster than a hundred eighty six
thousand miles per second
just to escape.
an impossible feat.
A black holes gravity is so huge because
it is a infinitely large mass
which has been compressed to be infinity small, making it extremely dense.  
Anything can become a black hole if you compress it down to its Schwarzschild radius.
This radius determines the size of a sphere, different masses need to be compressed to,
in order to become a black hole. 
If you wanted to make the earth into a black hole, 
we would need to crush all of it's mass down 
so that it would have  Schwarzschild radius of about 9mm
about the size of a marble. 
If we wanted to crush all the mass of the sun down, to make it a black hole. 
It would have a Schwarzschild radius of about 2.5km.
But what exactly lies within this radius?
