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

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

#91

Post by sliken »

pavel_lishin wrote: post #50
sliken wrote: post #22

Earlier quoted context omitted.

From the external view you never enter, just get dimmer as you approach the speed of light and the time dilation keeps increasing. From the viewpoint of the one falling in, you just fall in and cross the horizon without noticing. Does make you wonder if time dilation gets so extreme, could another black hole wonder by, offset the gravity of the black hole, and let you escape. Even if it takes a billion years.

Once you've crossed the horizon from your point of view, there is no escape. If another, larger black hole passes by, at best you'd be within a larger event horizon comprised of both, I think.

Right, but say you end up half way between two equal mass blackholes, under zero gravitational force. Are those two black holes definitely going to merge? If they were going near light speed in opposite directions could they not merge and free you as you stay equidistant from both?

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

#92

Post by sliken »

U1F984 wrote: post #43
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.

I can't find anything about these low gravity regions (Google redirects me to your post) but they sound interesting. Can you share some reading material?

Non-spinning and non-charged blackholes are called Schwarzschild or static black hole is a simple beast. You have a event horizon, a mass, and a slightly strange area near the event horizon where orbits are unstable, I believe within 1.5 times the event horizon distance.

Spinning blackholes (Kerr) of are quite complicated in comparison. They have an outer ergosphere, inner ergosphere, outer event horizon, and an inner event horizon. Also the singularity is no longer a point, but a ring.

A quote from the Ring_singularity link below:

  An observer crossing the event horizon of a non-rotating and uncharged black hole (a Schwarzschild black hole) cannot avoid the central singularity

  This is not necessarily true with a Kerr black hole. An observer falling into a Kerr black hole may be able to avoid the central singularity by making clever use of the inner event horizon associated with this class of black hole.
This is also explained in the Veritasium video at 1610 seconds: https://www.youtube.com/watch?v=6akmv1bsz1M&t=1610s

More info at:

  https://en.wikipedia.org/wiki/Rotating_black_hole
  https://en.wikipedia.org/wiki/Ergosphere
  https://en.wikipedia.org/wiki/Ring_singularity

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

#93

Post by andreareina »

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?

The innermost stable circular orbit is 3 radii for a non-rotating black hole, less the faster it spins.

https://en.m.wikipedia.org/wiki/Innermost_stable_circular_or...

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

#94

Post by andreareina »

idiotsecant wrote: post #73
BurningFrog wrote: post #69

Earlier quoted context omitted.

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?

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.

GP asked about (presumably free-falling) orbits, they are unstable before reaching the event horizon.

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

#95

Post by rthnbgrredf »

idiotsecant wrote: post #74
rthnbgrredf wrote: post #65

Earlier quoted context omitted.

Well, we have a pretty good understanding of how our sun works internally just by observing it from the outside, without ever digging a hole into it to observe it from the inside.

That's because the sun emits a great deal of information. Black holes by definition emit none (on human time scales)

The mentioned Hawking radiation is quite weak, weaker than we can currently measure, that's true. But for smalller black holes in the lab or for a black holes in our solar system (planet 9). It is very much possible (in the future) to detect the radiation and gain insights from it, maybe even within this century.

I would direct you to the holographic principle and the AdS/CFT correspondence. Because current theory suggest that the information that falls into a black hole is not lost and can be recovered (resolving the information paradox). Similar to as we can deduce the inner workings of the sun, from the information it emits, we could be able to deduce such information from hawking radiation in case of black holes.

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

#96

Post by zelphirkalt »

anal_reactor wrote: post #13
ganzuul wrote: post #11

Why is it that some experts say stuff falls into the center of a black hole while others say it slows down and never passes the event horizon? Is it just semantics?

The closer you are to the black hole the slower the time passes.

Why is that again? Falling in does not seem to imply accellerating towards the speed of light. Accellerating surely, but speed of light? Why would it?

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

#97

Post by dtech »

golem14 wrote: post #72
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.

I always wondered if you can orbit inside the event horizon of a large black hole and wait until its hawking radiation shrinks the event horizon so that you find yourself outside. You would have to wait a long time I guess.

"long time" here means several times longer than it will take for all stars to go out, so that's kinda an understatement

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

#98

Post by pavel_lishin »

sliken wrote: post #91
pavel_lishin wrote: post #50

Earlier quoted context omitted.

Once you've crossed the horizon from your point of view, there is no escape. If another, larger black hole passes by, at best you'd be within a larger event horizon comprised of both, I think.

Right, but say you end up half way between two equal mass blackholes, under zero gravitational force. Are those two black holes definitely going to merge? If they were going near light speed in opposite directions could they not merge and free you as you stay equidistant from both?

Well, if you're halfway and outside of hte event horizon... I don't know. But you definitely can't escape an event horizon.

I don't know what would happen if two event horizons overlapped briefly, as two black holes passed by each other at significant speeds. That's definitely above my paygrade :P

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

#99

Post by sliken »

pavel_lishin wrote: post #98
sliken wrote: post #91

Earlier quoted context omitted.

Right, but say you end up half way between two equal mass blackholes, under zero gravitational force. Are those two black holes definitely going to merge? If they were going near light speed in opposite directions could they not merge and free you as you stay equidistant from both?

Well, if you're halfway and outside of hte event horizon... I don't know. But you definitely can't escape an event horizon. I don't know what would happen if two event horizons overlapped briefly, as two black holes passed by each other at significant speeds. That's definitely above my paygrade :P

Well imagine you are X distance from the singularity, and time dilation is hugely slowing down time from an external observer. As blackholes approach each other, the distance between the singularity and the event horizon significantly decreases. They become kidney shaped before the blackholes merge.

The trick is can a blackhole approach quickly enough to catch you as you keep dropping as you past horizon. Normally I'd say no, but the time dilation significantly complicates things.

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

#100

Post by BurningFrog »

andreareina wrote: post #93
BurningFrog wrote: post #69

Earlier quoted context omitted.

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?

The innermost stable circular orbit is 3 radii for a non-rotating black hole, less the faster it spins. https://en.m.wikipedia.org/wiki/Innermost_stable_circular_or...

Thanks!
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