Undergrad Confusion about Frame Dragging

[Ibix]

Thanks, Ibix. so

I would end up spiraling into the black hole?

I wouldn't like to take a position on whether you would complete a full circle without doing some maths, but basically yes. If I drop you from a great distance from a non-rotating hole you will always be between me and the hole as you fall in. But with a rotating hole you would be dragged spinwards to some extent.

In practice the accretion disc around the hole would have a straightforward frictional drag effect as well (not to mention cooking you extra-crispy). I suspect that would tend to make you orbit more than a vacuum GR analysis would suggest, but I haven't done the maths for that either.

 

[nomadreid]

Many thanks for that, Ibix. That makes sense, even without the calculations. (The various things that can, as you put it, cook an astronaut extra-crispy, seem to do away with all science-fiction scenarios about an astronaut entering the event horizon alive.)

 

[PeterDonis]

Yesterday I learned that there may be ergospeheres around neutron stars too.

From where? Please give a reference.

 

[PeterDonis]

if there were no significant frame dragging around a supermassive black hole, then where do the jets of those who have them (OK, only a small portion, but nonetheless) come from?

The jets are believed to be coming out along the rotation axis of the hole; as I understand it, frame dragging basically collimates them to shoot out that way. But that is frame dragging considered globally, on the scale of the entire hole: as @Ibix said, that is very different from the difference in frame dragging between the feet and the head of an astronaut in a free-fall trajectory near the hole.

 

[tzimie]

From where? Please give a reference.

https://arxiv.org/pdf/astro-ph/0212429.pdf