First proof that "plunging regions" exist around black holes in space • Hacker News Board

Re: First proof that "plunging regions" exist around black holes in space

#101

Post by sliken » Mon, May 20, 2024, 7:33 PM UTC

squrky wrote: post #37

sliken wrote: post #21

Earlier quoted context omitted.

No need to perish, current theories explain that the innermost region of a spinning black hole (all real world black holes spin) has a low gravity region where arbitrary navigation is possible. You can't escape, but you also don't have a death date with the singularity.

My layperson understanding is that collision with the singularity (if that even exists) is mathematically inevitable for an object that has crossed the event horizon. I think your scenario of hanging out within the event horizon and safely away from the singularity for indefinite time would require infinite fuel to counteract the gravitational gradient, or for even more fundamental reasons.

For non-spinning blackholes (much like spherical cows that physicts use to simplify things) that's true.

For spinning blackholes not to much. The singularity turns into a ring, the center of which the gravity cancels out.

Re: First proof that "plunging regions" exist around black holes in space

#102

Post by sliken » Mon, May 20, 2024, 7:34 PM UTC

BurningFrog wrote: post #69

squrky wrote: post #37

Earlier quoted context omitted.

My layperson understanding is that collision with the singularity (if that even exists) is mathematically inevitable for an object that has crossed the event horizon. I think your scenario of hanging out within the event horizon and safely away from the singularity for indefinite time would require infinite fuel to counteract the gravitational gradient, or for even more fundamental reasons.

You can orbit a black hole like any other gravity source, without spending fuel. I don't know how near the event horizon a safe orbit can be?

No stable orbits exist within 1.5 x the event horizon radius, so just outside that should suffice, just watch for anything else falling in.

Re: First proof that "plunging regions" exist around black holes in space

#103

Post by sliken » Mon, May 20, 2024, 7:40 PM UTC

kelseyfrog wrote: post #47

chungy wrote: post #6

Earlier quoted context omitted.

We can hypothesize, but there is no known way to ever test it. At least not with the information getting out of the black hole.

Without being able to test, the insides of blackholes are outside the realm of falsifiability and thus forever beyond science.

Maybe, but if we found or made a tiny black hole, something could be beyond the event horizon just before it evaporates.

Or maybe spin it fast enough so the singularity is visible.

Re: First proof that "plunging regions" exist around black holes in space

#104

Post by sliken » Mon, May 20, 2024, 7:44 PM UTC

knodi123 wrote: post #33

pests wrote: post #14

Earlier quoted context omitted.

Frame of reference. The object falling in experiences time as normal and actually falls in. From an outside observer they never cross the event horizon, due to the time dilation mentioned by the other comment.

> From an outside observer they never cross the event horizon, due to the time dilation mentioned by the other comment. Doesn't that imply that if we look at a black hole from a safe distance, the event horizon will appear to be a cluttered frozen motionless ring, full of all the stuff that is in the process of falling in but which from out point of view, never will?

Sort of, the red shift continues towards infinity, but since photos are quantitized there is a last photon.

Also don't forget even if you freeze forever as viewed by an external observer, the blackhole is growing, and will at some point consume everything that had previously fallen in.

Re: First proof that "plunging regions" exist around black holes in space

#105

Post by idiotsecant » Tue, May 28, 2024, 2:51 PM UTC

lambdaxyzw wrote: post #85

idiotsecant wrote: post #73

Earlier quoted context omitted.

That's kind of the definition of the event horizon. You cannot be 'safe' once you're inside. All paths lead to the event horizon. No matter which direction you point, you're pointed at it.

I am not too knowledgeable about black hole physics, but it was my understanding that there's nothing locally interesting about event horizon: it's just the point of no return that doesn't change much for the local observer. Your definition of the event horizon make it sound more locally important. In fact, I know that as a local observer falling into a black hole you can still see some of the outside world after fal…

All paths point singularity-way but a cone will also see a false image from in falling photons. That cone will get smaller the further in you fall. That doesn't mean you aren't pointed at the singularity, only that some photons are going faster than you. It's like saying that because some traffic on the highway is passing you, you're actually going backward.

All paths inside the event horizon lead to singularity. Full stop. This is reinforced by the Penrose diagrams you mention.