zlacker

What teachers tell you in school is that as you get close to a uniform sphere the gravitational force increases with the square of the distance to the center of such sphere.

What they don't tell is that once inside the sphere the force decreases linearly, because the planetary mass ahead of you is partially balanced by the mass behind you.

With this you can see that the gravitational pull of a planet/start/spheroid is largest at its surface. So, if something happens to make a start shrink by some factor, the gravity pull at its surface is increased by the square of this factor, even if the mass of the star remains the same.

Actually I believe starts eject a lot of mass when they become black holes, and this is just a Newtonian argument for a phenomenon intrinsically relativistic, but I hope you get the gist of it.

>>emblae+(OP)
Yeah - a lot of mass gets 'blown away' which really made it even stranger that gravity increased. While I found your explanation illuminating, I still don't see how you can end up with 'more' gravity then you started with? Mass determines gravity right ? not volume ?