Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Beeskee]

The event horizon is the point where the escape velocity becomes greater than the speed of light. That happens when everything is all bunched up. If it was spread back out (like it was when the black hole was a star) it wouldn't be a black hole any more.


Damn, I hijacked my own thread.

[Il Palazzo]

Wait...I thought the event horizon was a gravitational field effect generated by the singularity. I'm trying to conceive how you would have an object that projects outside of its own gravitational field.

From what I gathered from the few articles I've found on the net, naked singularity hypothesis is as close to reality as the superstrings.
The wiki's article on these is not quote worthy, as it's got a huge headline saying "this article needs an attention fom an expert on the subject".
Apparently, Hawking is disagreeing with physical possibility of NS's existence, even though he concedes that it's mathematically provable.
I have not found anything describing the hypothesised process of "sheding the EH" in such a way as Beeskee's.

Articles I've found so far(anyone subscribes to Scientific American?)
http://www.astroengine.com/?p=6135
http://www.newscientist.com/article/dn12707-is-a-naked-singularity-lurking-in-our-galaxy.html

I'm pretty certain that nobody here can understand the particulars:
http://iopscience.iop.org/1742-6596/31/1/054/pdf/jpconf6_31_054.pdf

[RedKing]

Okay, so I just browsed the summary for rotating black holes, and I think I've got the gist. Actually, it kinda dovetails nicely with that original idea in the thread about using the earth's gravitational field as a slingshot. Same concept, just drastically different scale.

Basically, it should (in theory) be possible to dive into a rotating black hole and transit through it in a chord without actually contacting the singularity at its core and come back out. You could break the escape velocity issue because space-time would be so warped in the vicinity of the black hole that you could exceed the speed of light. The kicker is that you don't just come out of the black hole at an insanely high speed, but that you might also come out in a different temporal vector (i.e. time travel) and/or in a different location altogether (white holes).

The trick is that a rotating black hole creates two event horizons, and the narrow overlap between them creates an area where the gravitational pulls negate each other enough to survive. But the navigable aperture would be extremely tiny, 180 meters for a 17.7km diameter black hole. And the "opening" where the aperture begins is rotating with the black hole. And the black hole may be rotating at nearly the speed of light itself.


It would be like trying to shoot yourself through a doggy door mounted on a revolving door which is rotating 1000 times a second.

[Akigagak]

It would be like trying to shoot yourself through a doggy door mounted on a revolving door which is rotating 1000 times a second.

You know what? Sigged.

[Beeskee]

Apparently, Hawking is disagreeing with physical possibility of NS's existence, even though he concedes that it's mathematically provable.
I have not found anything describing the hypothesised process of "sheding the EH" in such a way as Beeskee's.

Anything squeezed down past the Schwarzschild radius would form an event horizon. Something with the mass of the Earth would become a black hole if it was squeezed down to the size of a pea. If it were stretched back out, it would lose the event horizon.

Naked singularities are unlikely to occur naturally. Even colliding black holes wouldn't be likely to form one.


Making one of these things is a mega project for an advanced civilization, one that has an entire galaxy's worth of energy to work with already.

For us, it's all still science fiction.


Edit: And yeah, I wouldn't try to fly through it.

[Il Palazzo]

What I'm trying to say here, is that I've not found any mention of a process that would "stretch" a singularity, and especially to stretch it enough to emerge from it's event horizon.
What you seem to describe as the process leading to a naked singularity formation, is that the spinning singularity stops being a point-like discontinuity in space-time, and becomes a ring/torus-like entity, stretched to the point when it's radius is larger than the event horizon's, while still retaining the properties of a singularity, which should include infinite density, and looks very much like a logical fallacy.(as DJ noted before)
The fallacy lies in the fact that every, infinitesimally small "bit" of the toroidal singularity should still have infinite density, and so, bend the spacetime enough to create the event horizon in it's neighbourhood.

Correct me if I got your reasoning wrong.

[Beeskee]

The singularity has infinite density but not infinite mass. It's the mass that determines the Schwarzschild radius and where it lies. Rotation would stretch the singularity. If the mass is outside the radius then there's no event horizon.

As to HOW to 'spin up' a black hole: Like I said, that's a project for an advanced civilization.

And yes, it's all theoretical, the advanced civ may just end up with a doughnut shaped black hole and a lot of energy down the drain.


This describes rotating black holes in more detail: http://en.wikipedia.org/wiki/Rotating_black_hole


And from the page on Gravitational Singularities: While in a non-rotating black hole the singularity occurs at a single point in the model coordinates, called a "point singularity", in a rotating black hole, also known as a Kerr black hole, the singularity occurs on a ring (a circular line), defined as a "ring singularity".

In brief: Non-rotating black holes have point source singularities, rotating ones have ring singularities.

[RedKing]

But...you can't have infinite density if the singularity actually has three dimensions. You might have obscenely high density, sufficient even to create an event horizon, but it couldn't mathematically be infiinite.

A singularity has infinite density because it has no volume. It's the universe dividing by zero. What we term a "black hole" is the field around the singularity where the escape velocity is larger than the speed of light. For a stationary point singularity, this should be spherical and by definition, encompass the singularity in all directions.


The only possible scenario I can envision is a two-dimensional ring which would then still lack volume, but it's difficult to conceive how such an object would exist without collapsing itself back into point singularity under its own gravitation. And it should produce a toroidal black hole which would still fully envelop the ring singularity. There might be some sort of bizarre "aperture" in the middle of the ring where opposing gravitational pull cancels out (no doubt with reality-warping characteristics) but the aperture would be extremely tiny, possibly even a point singularity itself. And now we're describing something more like a stargate than a black hole.

[Eagleon]

Whenever time travel comes up, I always wonder why time loop computation or communication doesn't. That is, using a loop to send processed information into the past, to be reprocessed ad infinitum. Violates the same stuff in physics, and you could do so much more with it, up to and including simulating entire universes depending on how many times over you could do it.

[Il Palazzo]

The singularity has infinite density but not infinite mass. It's the mass that determines the Schwarzschild radius and where it lies. Rotation would stretch the singularity. If the mass is outside the radius then there's no event horizon.

My beef with your description of the subject is that it doesn't seem to hold under close scrutiny. For example, when your singularity stops being equivalent to a material point, you can't carry on treating it as such for the purposes of event horizon shape and extent calculations.
Considering a "part" of the supposed ring-like singularity(infinitely small, for ease of calculations), it will always create an event horizon around itself, however tiny it could be. How much mass exactly it has doesn't matter, since it's infinitely dense. Neither does it matter what other parts of the ring "do", as gravitational fields do not affect each other(apart from adding up).

As to HOW to 'spin up' a black hole: Like I said, that's a project for an advanced civilization.

This is actually quite easy, in fact, it's happening all the time - any mass falling into a black hole carries some angular momentum, that remains conserved by speeding up(or slowing down) the singularity's rotation.

[MetalSlimeHunt]

Given how the Milky Way may or may not be structured, everything in this galaxy could be falling into a Supermassive Black Hole as we speak, just very slowly by our standards.

[Il Palazzo]

Given how the Milky Way may or may not be structured, everything in this galaxy could be falling into a Supermassive Black Hole as we speak, just very slowly by our standards.

It's a common misconception about black holes, that everything must fall into one, once it gets into a vaguelly defined "vicinity" of such a body.
Stuff is actually quite content with endlessly orbiting around a black hole. Once it cleared the space around itself off of whatever had too little angular momentum to enter an orbit, it's just another massive body in space, like e.g. the Sun. Nobody's falling into the Sun. Not without outside help, at least.
[/Palazzo_nitpicking_again]

[MaximumZero]

So, wait, to make a black hole go faster, we throw stuff into it? Do you know what this means!?

Now we have an excuse to! What are we waiting for?

[Pandarsenic]

Nobody's falling into the Sun. Not without outside help, at least.

A little effort could solve that.

[MetalSlimeHunt]

Given how the Milky Way may or may not be structured, everything in this galaxy could be falling into a Supermassive Black Hole as we speak, just very slowly by our standards.

It's a common misconception about black holes, that everything must fall into one, once it gets into a vaguelly defined "vicinity" of such a body.
Stuff is actually quite content with endlessly orbiting around a black hole. Once it cleared the space around itself off of whatever had too little angular momentum to enter an orbit, it's just another massive body in space, like e.g. the Sun. Nobody's falling into the Sun. Not without outside help, at least.
[/Palazzo_nitpicking_again]

...which is why I added that this may or may not be the case. In any case, everything must indeed fall into a black hole once it reaches a vaguely defined vicinity, that being the event horizon. Of course, even the largest black hole wouldn't have an event horizion over the whole Milky Way.

Gah, I hate typing about black holes. They break reality and it hurts my head.

So, wait, to make a black hole go faster, we throw stuff into it? Do you know what this means!?

Now we have an excuse to! What are we waiting for?

Faster? Not really. I don't think black holes can move. But black holes do grow if things are thrown into them, offsetting the Hawking radiation that slowly destroys them. You know, black holes act eerily like living beings under that context...