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Fraser
2007-Sep-25, 06:20 PM
Black holes are already plenty bizarre. Imagine all the mass of several suns compressed down into an object of potentially infinitely small size. But what if you could find an object that's even stranger: ...

Read the full blog entry (http://www.universetoday.com/2007/09/25/searching-for-objects-even-stranger-than-black-holes/)

Hlafordlaes
2007-Sep-26, 11:54 AM
"Once the object reaches a certain size its pull becomes so great that nothing, not even light can escape"

Confess I've always had trouble with this. My understanding is that it is the spacetime curvature created by the black hole that traps light, not its gravity outright, as light is not affected directly by gravity's pull. Or is it? The wording of this article seems to suggest it is.

Don Alexander
2007-Sep-26, 12:31 PM
My friend, in General Relativity, space-time curvature IS gravitation. Light is affected by gravity (gravitational lensing), as it follows curved pathes in space-time. This effect is also predicted by Newtonian gravity + light-as-particles theory, but the Einsteinian effect is twice as large, showing that general relativity is correct.

Alex

John Mendenhall
2007-Sep-26, 12:43 PM
And all real collapsed objects spin, and as they collapse, they spin faster and faster, and . . .

GOURDHEAD
2007-Sep-26, 01:32 PM
And all real collapsed objects spin, and as they collapse, they spin faster and faster, and . . .Are we certain that spin and charge mean the same thing inside a black hole as they do outside, or whether the radius of the singularity is truly zero (non-spinnable) or just vanishingly small, or how fast an object can "fall" from where the event horizon should have been to the singularity? Assuming the "singularity" has a non-zero radius and that the black hole spins up such that the tangential velocity of the particle is less than that of light by a vanishingly small amount, is the energy of the angular momentum, if such exists, of the black hole transferrable to the relativistic mass of the particle and eventually to pair annihilation radiation?

rswarbrick
2007-Sep-26, 01:47 PM
Hi! I often like to read the papers published in this sort of story too - for this one there is a publicly available preprint in the Arxiv: http://arxiv.org/abs/0706.0132.

Maybe it would be possible to include doi or arxiv links to some of these stories?

Grand_Lunar
2007-Sep-27, 02:26 AM
A black hole that's not black?

Hmmm, what to call it. White hole is already used. Maybe a gray hole?

stellark
2007-Sep-27, 11:09 AM
But in theory, if you could get a black hole spinning ludicrously fast, so that the angular momentum of its spin overcomes the gravitational pull of its mass, it should be able to shed its event horizon. A black hole with 10 times the mass of our Sun would need to be spinning a few thousand times a second.

Why hasn't this been considered before now? :liar:

This is weird! :think: I'm reminded somehow of the '50s movie "Earth Vs The Flying Saucers"... spinning objects counteracting gravitational fields... lol!

John Mendenhall
2007-Sep-27, 02:12 PM
Why hasn't this been considered before now?



Because the math is truly horrible, and causes squabbles even amongst the mathematicians. As I recall, Michio Kaku has a section in one of his books describing sitting down with 10 other physicists and working for 12 hours straight going over a proof to make sure there was no mistake in it. The multiple tensors (10) in GR can be very difficult to interpret; and they are simultaneous, what's going on in one affects the others. The static black hole case (the Schwarzchild solution) is well studied because it's one of the easier ones. See the Wiki GR and SR articles, they're good.

curry
2007-Sep-27, 02:47 PM
It is the singularity that is spinning, not the event horizon. The event horizon is not some object that is going to fly away from spinning. It is only the distance from the singularity where the gravity is strong enough to bend light back to the singularity. I have doubts about this idea.
Angular momentum of a spinning singularity might expand the size of the singularity. This is just another reason to doubt that a singularity is a point with no space or any infinite anything. Something is wrong with dividing by zero to get infinity. Oh, it's the math.

Fortunate
2007-Sep-28, 06:59 PM
Hi! I often like to read the papers published in this sort of story too - for this one there is a publicly available preprint in the Arxiv: http://arxiv.org/abs/0706.0132.

Maybe it would be possible to include doi or arxiv links to some of these stories?

Thanx for the link. Fraser's article (and a similar one on physorg.com) left me with the impression that the authors were proposing the existence of naked singularities. The link provided by rswarbrick seems to indicate that the arxiv article merely outlines a method for determining the ratio of angular momentum to mass (for black holes) from observations of gravitaional lensing. This determination sounds very interesting for its own sake.
The contention that a/m>1 would indicate a naked singularity, then, does not, at first sight, seem to be a prediction that this situation would or even could ever actually occur.

Fortunate
2007-Sep-28, 07:34 PM
O.K., I read the first two pages of the arxiv article and hereby renounce my last post.

howard2
2007-Sep-28, 07:44 PM
Can there be anything more dangerous and frightening than a naked singularity?

curry
2007-Sep-28, 09:26 PM
Spinning a blackhole (singularity) could never cause it to shed it's event-horizon: the energy associated with the spinning counts towards the mass-energy used to determine the size of the event horizon. The faster the blackhole spins, the large the event horizon. It is the singularity that spins. The event horizon is only the distance where the gravity is great enough to bend light back to the singularity.

curry
2007-Sep-28, 11:45 PM
"Can there be anything more dangerous and frightening than a naked singularity?"
Putting aside my disbelief that you could even have a singularity without an event horizon. Since a lot of mass (ie: gravity) is pushed away when a star contracts to form a black hole (singularity), the star that formed the black hole had more mass and gravity than the singularity. The original star would be more dangerous than the singularity it formed.

RUF
2007-Sep-29, 01:21 AM
Hmmm, what to call it. White hole is already used. Maybe a gray hole?

A Bright Hole?

Kootenaistar
2007-Sep-30, 09:51 AM
I don't often get into the forums, but wish to make a comment, perhaps not great here. I'm older and/or less educated in the math and theory of astronomy, but I learn a lot from your discussions and even understand other articles better. Thanks.:)