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this post was submitted on 28 Sep 2023
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The title kind of misses the point: of course it spins; it would be remarkable if it didn’t.
The really interesting bit is how relativistic frame dragging is causing its spin axis to precess.
(Also, the illustration conflicts with the description: it shows the whole accretion disk wobbling instead of just the jets.)
Can you ELI5 relativistic frame dragging and process?
Frame dragging is when matter drags spacetime along with it. Roughly think of a the wake of a boat disturbing other things in the water.
The misalignment of the black holes axis of spin, and the axis of the accretion disk is causing interesting frame dragging effects.
Does the black hole spin? Or does the stuff outside the black hole spin? 🤔
The black hole and the stuff outside it constitute a single system, and within that system, angular momentum is conserved. So as objects cross the event horizon, their angular momentum is transferred to the black hole.
Well.... does it? If all the stuff falls in and only the volume remains, who could say that it's spinning? How could you detect it?
For one thing, the size and shape of the event horizon change depending on the black hole’s spin.
What would happen if one were to stop spinning? Could one even stop spinning?
Yes—it’s called the Penrose process.
I see. Thank you. So, you can use light to infer the mass, and then the volume information to infer the spin? Easy enough.
That would be a general method, if we were close enough to observe the shape of the event horizon (which we aren’t).
The article is describing another way, which only works in this case because the black hole is precessing so extremely that the changing axis of rotation is frame-dragging the polar jets along with it.
I thought nothing actually crossed the event horizon and was essentially frozen approaching a complete stop in time in a kind of 2f representation of 3d reality until it slowly leaked out trillions of years later as hawking radiation?
From an outsider's perspective, you would see an object approach and then freeze. It would red-shift dimmer until it disappeared. From an in-falling perspective, I don't think you'd notice anything at all.
Isn’t most everything spinning? Seems like having zero angular momentum would be rare and remarkable. I’m not even sure how exactly to define zero momentum in terms of reference frames.
If you're asking that then you first need to ask what the distinction between the two is. and further does it even make sense for one to spin and not the other
Is there not a distinction? I assume the singularity at its center has different properties than the matter outside of that point.
Note: I have a rudimentary understanding of what black holes and their components are.
Even if there is heterogeneity inside the system, that does not indicate severability or that the whole system is made up of smaller constituent systems.
Yes.
It's in space and everything is relative, how do we know *everything else" isn't just spinning around the black hole? 🤔
Because that would require a centripetal force on everything else, which obviously isn't the case.