Warning nerd sniper!

[NTP2]

What if a large space craft was orbiting just above the event horizon of a black hole then a astronaut went on a EVA and went past the event horizon, but then some else tried to pull them back.

Ps the astronaut has a tether.

PPs my first answer was that the line breaks but since orbital velocity is lower than escape velocity they should still be in a lower (but faster) orbit.

 

[Antares JS]

Spaghettification happens. The astronaut who crossed the event horizon has been ripped apart down to his molecules and is already dead. And this is ignoring the effect of time dilation in a massive gravity well and assuming that your ship is made of some kind of super-stretchy material that doesn't also get ripped apart by gravitational tidal forces.

 

[NTP2]

Spaghettification happens. The astronaut who crossed the event horizon has been ripped apart down to his molecules and is already dead. And this is ignoring the effect of time dilation in a massive gravity well and assuming that your ship is made of some kind of super-stretchy material that doesn't also get ripped apart by gravitational tidal forces.

That does disrupt my thought experiment, move the ship up to a safe distance and make the string from something that wouldn’t break and remove the thing at the end, the main thing is that I was wondering how escape velocity is working in that situation since you’re escaping but not at the velocity.

 

[Azamiryou]

Spaghettification happens. The astronaut who crossed the event horizon has been ripped apart down to his molecules and is already dead. And this is ignoring the effect of time dilation in a massive gravity well and assuming that your ship is made of some kind of super-stretchy material that doesn't also get ripped apart by gravitational tidal forces.

If the black hole is big enough, the tidal forces aren't strong enough for spaghettification at the event horizon.

I suspect the real answer (assuming a big enough black hole to avoid spaghettification) is something really weird. Mathematically, dimensions get flipped around inside the event horizon, so the ship outside tugging in a spacial dimension will exert its force on you in the time dimension. I have no idea how you would experience that, though.

 

[Antares JS]

That does disrupt my thought experiment, move the ship up to a safe distance and make the string from something that wouldn’t break and remove the thing at the end, the main thing is that I was wondering how escape velocity is working in that situation since you’re escaping but not at the velocity.

Assuming nothing breaks, once a part of your ship has gone past the event horizon, the escape velocity is greater than the speed of light. If you can't pull it out faster than the speed of light or cut that string, it's going to drag the rest of your ship into the event horizon.

That's my best guess.

 

[Rschub]

Look at Space Elevators for a less disgronificating example.

 

[Azamiryou]

I was wondering how escape velocity is working in that situation since you’re escaping but not at the velocity.

A fair question. Escape velocity is how fast you need to go to escape a gravity well in free fall. If you're being acted on by other forces, like thrusters or being pulled by a tether, you can escape at any non-zero speed.

At least in normal space, that is. What about inside an event horizon?

I suspect either (or both)
A) the dimension switch means the force applies to time rather than space and you can't change the spacial trajectory of something inside
B) the minimum amount of energy required to escape a gravity well is always the same. Perhaps inside the event horizon, this minimum amount of energy is infinity.

 

[Hobie1dog]

Imminent death.

 

[NTP2]

I suspect the real answer (assuming a big enough black hole to avoid spaghettification) is something really weird. Mathematically, dimensions get flipped around inside the event horizon, so the ship outside tugging in a spacial dimension will exert its force on you in the time dimension. I have no idea how you would experience that, though.

Ohh good point!! I’ll subscribe to this idea.

B) the minimum amount of energy required to escape a gravity well is always the same. Perhaps inside the event horizon, this minimum amount of energy is infinity.

Maybe, I don’t see why as it’s still orbiting just faster.

 

[Antares JS]

Maybe, I don’t see why as it’s still orbiting just fafaster.

Like I said, the definition of the event horizon is the point at which escape velocity becomes faster than the speed of light.

 

[NTP2]

Like I said, the definition of the event horizon is the point at which escape velocity becomes faster than the speed of light.

You should know this, escape velocity is the velocity required to leave the gravity well (technically you’re always in it it’s just so small it’s nonexistent) orbit is much smaller eg 8 kps for orbit but 11 for escape. The same applies to a black hole.

 

[Antares JS]

You should know this, escape velocity is the velocity required to leave the gravity well (technically you’re always in it it’s just so small it’s nonexistent) orbit is much smaller eg 8 kps for orbit but 11 for escape. The same applies to a black hole.

Yeah, I do know that. And the fact that the escape velocity beyond the event horizon is faster than the speed of light is the reason why the energy needed to achieve escape velocity is infinite, like @Azamiryou said.

 

[NTP2]

Yeah, I do know that. And the fact that the escape velocity beyond the event horizon is faster than the speed of light is the reason why the energy needed to achieve escape velocity is infinite, like @Azamiryou said.

That isn’t what I was saying, I meant that you can orbit inside the event horizon, I agree that you can’t leave.

 

[Antares JS]

That isn’t what I was saying, I meant that you can orbit inside the event horizon, I agree that you can’t leave.

I read somewhere that once past the event horizon, there is nowhere you can go but down, but I'm not sure if that's correct or possibly outdated information.

 

[Jeff Lassahn]

So, the Wikipedia article on "Event Horizon" (https://en.wikipedia.org/wiki/Event_horizon) has the answer:

In the case of the horizon around a black hole, observers stationary with respect to a distant object will all agree on where the horizon is. While this seems to allow an observer lowered towards the hole on a rope (or rod) to contact the horizon, in practice this cannot be done. The proper distance to the horizon is finite,[21] so the length of rope needed would be finite as well, but if the rope were lowered slowly (so that each point on the rope was approximately at rest in Schwarzschild coordinates), the proper acceleration (G-force) experienced by points on the rope closer and closer to the horizon would approach infinity, so the rope would be torn apart.

A few other random facts:
There's a distance outside the event horizon where escape by actively accelerating is possible, but there aren't any stable orbits. So "orbiting just above the event horizon" is not a thing.

As an object approaches the event horizon, time dilation goes to infinity, so the astronaut and the ship disagree by an infinite amount about how long the trip takes. That means among other things that if the ship is in orbit and the astronaut is going straight down, the rope gets wound around the black hole an infinite number of times.

The mathematical solution where the time and space dimensions get flipped at the event horizon is very misleading. The solution inside the event horizon is valid, the solution outside the event horizon is valid, but the solution exactly on the event horizon fails. The two pieces don't actually connect up the way it looks like they do. There's no path that a real object could follow that passes between the two regions without the math going bad. There are other solutions in other coordinate systems that don't have this problem and they're way more useful for understanding what it's actually like to cross the event horizon. (for example https://en.wikipedia.org/wiki/Kruskal–Szekeres_coordinates)