system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a black hole have more gravity than the star that created the black hole?

A black hole is born from a very massive star.  Let's say this star has a mass of x.  

When the star goes supernova, it's basically explodes most of the mass into space.  The core, however, is condensed into a black hole.  This black hole has a mass < x, yet the gravity of the black hole is > x.  We know this because the star wasn't sucking light into it, but the black hole is.

How can this be?
gpt
Imagine that space time is like a sheet of rubber and the star is like a 100lb weight the size of a beach ball placed on the sheet. The mass of the 100lbs bends the sheet downward putting a dimple in it. The dimple is angled gently the farther out from the weight, but gets steeper as you get closer to the weight. 

Now imagine you put a different 100lb weight on it but this one is the size of a marble. You have the same mass, but it's in a more compact size now, so it will make a dimple that is even deeper than the first, and the angle will be much steeper. 

Basically the more concentrated the mass, and the smaller the space it occupies, the more it bends space time next to it, and the steeper this curve becomes. It's not that a black hole has more gravity, it's that the change is more abrupt and it bends space time more severely in a smaller area. 

Mathmatically we can describe this as the force of gravity being proportional to the square of the distance. Go twice as close to the object, and the gravitational force is 4 times as much. Move 4 times closer to it and the force goes up 16 times. Because black holes are so small, you can get much closer to their gravity well. At the point past the event horizon, the force of gravity is so strong that light can't escape. 

What is interesting is that a black hole can be almost any size. It's not the mass of the object that matters, it's how large it is in proportion to that mass. We call this the Schwarzschild radius. Basically what this radius represents is the amount of mass you would need to have inside of a sphere of a given size in order for it's escape velocity to equal the speed of light. For instance if you could somehow squeeze the earth down to about the size of a marble, it would be a black hole with the mass of the earth instead of the mass of a star. It wouldn't start devouring the sun or anything, and even the moon would keep right on orbiting the tiny little black hole. But anything that got too close to that tiny little singularity would be devoured and spaghetified just like any other black hole. 


- Edit  there are a lot of questions about why the size matters and not the mass. If you could fall through a hole cut in the center of the earth, you would fall very fast, but as you got deeper in, the gravitational pull of all the rock above you, would help to cancel out the pull of the rock below you, slowing you down. If you made it to the center of the planet, you would be weightless as you would be pulled in every direction equally. 


Lets do this as a thought experiment. Lets say you have 40 guys arranged in a circular shape and they all had a rope tied to you. in different spots and tried to pull you towards them. Once you passed into the circle, some would be pulling you in towards the center, but the ones behind you on the edge would be trying to pull you back out. In fact you might even be strong enough to walk through the circle and walk out the other side 'escaping'. 

The larger this circle of 40 guys is, the easier it is to defy their pull because spreading them out has them pulling you from many different directions. 

Now what happens when those 40 guys all jump in a manhole but their ropes are still pulling you? Now no matter how close you get to them, the force pulling you doesn't let up. And all those ropes are going to the same spot, pulling you towards the same spot, and if you tried to walk away, instead of the ropes being spread out, they are all pulling you the same way so you can no longer walk back out, you are trapped, spiraling inwards towards the hole in the center until you are pulled into the hole. 

Except it's not guys with ropes, it's large objects like a planet, exerting gravitational force on each other, and on other objects. When that force is spread out, it kind of comfortable. If that force were to be stuck in a single place and the pull of the entire planet was in a single direction, and the closer you got to that small spot, the harder it would pull you, that is a black hole.