developed, an idea developed by Karl Schwarzschild, a German scientist who was

actually working on this theory while serving in the trenches in the first

world war, Carl Schwarzchild developed the solution to Einstein's theory.

Sadly, died in the first world war due to disease,

and in his solution, it turns out you can work out what is the characteristic radius

that what we now call the Schwarzchild radius associated with the black hole.

And that Schwarzchild radius depends on the strength of gravity,

mass and the speed of light squared.

If you think about this as a Newtonian physicist and

think about light going around in an orbit around the black hole,

this would be the sort of characteristic radius you'd write down.

That's a pretty small radius for an object who's mass is the size of the Sun.

The Schwarzchild radius is about three kilometers.

So, you'd have to shrink the Sun down to the size of being much smaller

than the scale of Manhattan to collapse the sun into a black hole,

and make it curve space enough.