Planets Could Orbit Singularities Inside Black Holes

[KilljoyKlown]

I found this interesting article and I've never heard of an inner Cauchy horizon before. Is this really a possibility or is it a crack pot theory?

http://www.technologyreview.com/blog...26626/?ref=rss

The discovery of stable orbits inside certain kinds of black hole implies that planets and perhaps even life could survive inside these weird objects, says one cosmologist

It's easy to imagine that black holes gobble up everything they encounter, consigning this stuff to eternal oblivion. Right?

Well, not quite. Today, Vyacheslav Dokuchaev at the Institute for Nuclear Research of the Russian Academy of Sciences in Moscow points out that certain black holes can have a complex internal structure. And that this structure ought to allow photons, particles and perhaps even planets to orbit the central singularity without ever getting sucked all the way in.

A black hole is a region of space where gravity is so strong that nothing can escape, not even light. However, cosmologists have known for some time that there are regions inside charged, rotating black holes where objects such as photons can survive in stable periodic orbits.

Dokuchaev's contribution is to study these orbits in detail and to explore their dynamics. One of the problems that would at first seem to scupper any chance of planetary orbits inside a black hole is the way that the dimensions of space and time behave.

It's well known that a traveller passing through a black hole's event horizon arrives in a region in which the radial dimension becomes time-like, rather than space-like. Conventional orbits are clearly impossible here.

But travel further in and there is another horizon where the dimensions switch back again (at least, inside charged and rotating black holes). This is the inner Cauchy horizon and it's beyond here that Dokuchaev says the interesting orbits for massive planets exist.

He calculates that the stable orbits are nonequatorial and have a rich structure (see picture above). They would also be brightly illuminated by the central singularity and by photons trapped in the same orbit.

That raises an interesting question: whether a planet in such an orbit could support a complex chemistry that is rich enough to allow life to evolve.

Dokuchaev clearly thinks so. "Advanced civilizations may live safely inside the supermassive BHs in the galactic nuclei without being visible from the outside," he says, somewhat speculatively.

Of course, such a civilisation would have to cope with extraordinary conditions such as huge tidal forces and the huge energy density that builds up in these stable orbits as photons become trapped. There's also the small problem of causality violations, which some cosmologists predict would plague this kind of tortured space-time.

Dokuchaev has taken an interesting idea and pushed it as far as he can. It's one I suspect readers can have a lot of fun with too.

[siphra]

Personally I doubt this, but then again, I am no cosmologist.

[Dywyddyr]

Damn!
I bet Bob Forward could have made a bloody good story out of that. Right up his street.

[KilljoyKlown]

Damn!
I bet Bob Forward could have made a bloody good story out of that. Right up his street.

This theory only works for black holes with high rotation speeds. I'm not sure what percentage of black holes rotate and what kind of rotation speeds we are talking about. I have heard a theory that says it's possible for a black hole to achieve faster than light rotation speeds. Again I'm not sure how that could happen if it does.

[YoYoPapaya]

This theory only works for black holes with high rotation speeds. I'm not sure what percentage of black holes rotate and what kind of rotation speeds we are talking about. I have heard a theory that says it's possible for a black hole to achieve faster than light rotation speeds. Again I'm not sure how that could happen if it does.

I wonder what would be the nature of the entrance of our universe into the black hole seen from inside the black hole universe.

[tashja]

I wonder what would be the nature of the entrance of our universe into the black hole seen from inside the black hole universe.

AlphaNumeric said, and I quote: '' a black hole would first rip you apart due to tidal forces and vaporise you due to time dilation effects making the universe outside the black hole appear to get brighter and hotter without bound.''

[siphra]

I wonder what would be the nature of the entrance of our universe into the black hole seen from inside the black hole universe.

I would imagine it would be bright, very bright as all the photons trapped by it are just swimming around, instead of the black of our universe background.

[KilljoyKlown]

AlphaNumeric said, and I quote: '' a black hole would first rip you apart due to tidal forces and vaporise you due to time dilation effects making the universe outside the black hole appear to get brighter and hotter without bound.''

The article is only talking about super massive black holes for which the title forces don't manhandle you like the smaller stellar size BH's do, and once you cross the event horizon there are no longer any time dilation effects or so the theory says.

[tashja]

Of course, such a civilisation would have to cope with extraordinary conditions such as huge tidal forces and the huge energy density that builds up in these stable orbits as photons become trapped.

[KilljoyKlown]

I didn't say there wouldn't be title force problems, just that the effects are quite different for the different size BH's. Also I personally find it very hard to believe any life could exist on the other side of an event horizon of any size BH. Anyway if life could exist on the other side of the event horizon, we would never be able to know about it would we?

[CptBork]

There's also the small problem of causality violations, which some cosmologists predict would plague this kind of tortured space-time.

When you mentioned this, it reminded me of an interesting historical fact. The famous logician Kurt Godel was a personal friend of Einstein's and actually quite well-versed in General Relativity. On top of all the things he's famous for in mathematics and logic, Godel was also the first to discover closed timelike curve solutions to the GR equations inside black hole event horizons (i.e. particles from the future interacting with themselves in the past). Of course this represents an idealized solution, neglecting everything in the universe other than the black hole itself and an infinitesimally light particle inside the event horizon which doesn't contribute anything to the total gravity. It also doesn't take quantum mechanics into account, which might potentially solve the entire conundrum.

[Pinwheel]

Anyway if life could exist on the other side of the event horizon, we would never be able to know about it would we?

We could, if we ventured past the event horizon ourselves.

[KilljoyKlown]

We could, if we ventured past the event horizon ourselves.

Well I can't say I'm any more eager to do that than I want to put a bullet in my head.

[siphra]

Well I can't say I'm any more eager to do that than I want to put a bullet in my head.

Idk, If I could choose the way I die, falling into a black hole would be on the top of the list I think. Other than not dieing, that is.

[KilljoyKlown]

Idk, If I could choose the way I die, falling into a black hole would be on the top of the list I think. Other than not dieing, that is.

You can always choose a way to die, but getting to a black hole might be a problem.

If you could get into a very tight orbit around a BH and release a long wire so that one end of it would cross the event horizon, it should be possible for someone on the other side to now send you a message. My thinking here is that gravity doesn't affect electricity the same way it does light.

[RJBeery]

If you could get into a very tight orbit around a BH and release a long wire so that one end of it would cross the event horizon, it should be possible for someone on the other side to now send you a message. My thinking here is that gravity doesn't affect electricity the same way it does light.

This isn't possible. The integrity of the wire (regardless of strength, thickness, material, etc) would be compromised and break as it crossed the EH. There are forces holding those molecules in place which are all subject to the same extreme conditions that everything else is in the vicinity.

[KilljoyKlown]

This isn't possible. The integrity of the wire (regardless of strength, thickness, material, etc) would be compromised and break as it crossed the EH. There are forces holding those molecules in place which are all subject to the same extreme conditions that everything else is in the vicinity.

Okay, and a tight orbit might be a problem too. How fast would you have to be going to get within say a mile of the event horizon?

[RJBeery]

Okay, and a tight orbit might be a problem too. How fast would you have to be going to get within say a mile of the event horizon?

I believe the formula is v=c*sqrt(r_s/(2(r-r_s))). An orbital velocity of c would give you a stable orbit of 3/2 r_s, which would require a black hole with an r_s of 2 miles which I'm certain would have lethal tidal forces. In other words, orbiting 1 mile above the BH is not possible.

[KilljoyKlown]

I believe the formula is v=c*sqrt(r_s/(2(r-r_s))). An orbital velocity of c would give you a stable orbit of 3/2 r_s, which would require a black hole with an r_s of 2 miles which I'm certain would have lethal tidal forces. In other words, orbiting 1 mile above the BH is not possible.

That sounds like a fairly small BH. Would the same apply to a SMBH of a few million solar masses or larger? The way I understand tidal forces is the more massive the BH the less difference between the forces at the near and far side of an object will be.

[RJBeery]

Yes, it's the same formula, and yes the tidal forces can be made arbitrarily small by assuming a larger BH. Keep in mind that this is for a stable orbit with no active rocket acceleration. If you're thrusting your rockets away from the BH you could get closer to it. Regardless, you could never "go fishing" across the EH.