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- TL;DR Summary
- A light black hole has stronger surface gravity and tidal forces just outside the horizon than a supermassive black hole. Why can't light nevertheless escape just inside the horizon of the supermassive black hole?

As the summary says: a light black hole has stronger surface gravity and tidal forces just outside the horizon than a supermassive black hole. So if you want to hoover just outside the horizon of a black hole and care about your well-being it better be supermassive. I understand this perfectly from a GR-point of view and a Newtonian analogy. But somehow my intuition clashes with the fact that also for this supermassive black hole light can't escape from inside the horizon to the outside. In the large M limit you can make the surface gravity arbitrarily weak just outside the horizon while the horizon still prevents light to escape. Is my confusion the fact that the surface gravity is defined for an observer at infinity, and the amount of required thrust for a stationary observer right outside the horizon becomes incredibly high as is mentioned e.g. here,

https://www.mathpages.com/rr/s7-03/7-03.htm

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So, to give something concrete: is the following statement true? "A supermassive black hole has a smaller surface gravity right outside its horizon than a light black hole as measured by an observer far away, but the required thrust for an observer to stay stationary just outside the horizon is for a supermassive black hole much bigger than for a light black hole"

https://www.mathpages.com/rr/s7-03/7-03.htm

?

So, to give something concrete: is the following statement true? "A supermassive black hole has a smaller surface gravity right outside its horizon than a light black hole as measured by an observer far away, but the required thrust for an observer to stay stationary just outside the horizon is for a supermassive black hole much bigger than for a light black hole"