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Offline Airthumbs

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What shape is a Black Hole?
« on: 27/02/2011 01:09:22 »
This might sound like an obvious question or maybe not.  A Black Hole, what shape is it in 3 dimensional space?  Is it possible for example to approach one from behind?  Is the event horizon a completely spherical shape like most other gravitationally bound objects? (Planets, Stars, Quasars, Red Dwarfs and so on......)

I have this image of a black hole having a circular entrance leading down some long funnel ending up at the singularity but I assume that is from the gravitational representation of these objects?

I don't recall ever seeing what it would actually look like.  Maybe the singularity, which by the way has a point of zero g at the center, is more like the core of a spherical object.  Someone in this forum must have some ideas and maybe the Cambridge folk know something about this also :-)


 

Offline abacus9900

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What shape is a Black Hole?
« Reply #1 on: 27/02/2011 09:45:08 »
A black hole that does not rotate takes the shape of a single point. A rotating black hole is smeared out in space to form a ring. Both have zero volume but infinite density.
 

Offline yor_on

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What shape is a Black Hole?
« Reply #2 on: 01/03/2011 15:56:45 »
"A new theoretical investigation has recently determined that black holes can come in a myriad of shapes and sizes. The thing about this theory is that it cannot be proven or disproven, due to the fact that astrophysicists cannot actually investigate the shape of a black hole, or any other of its properties. The structures attract all manner of radiation, including visible light, and so gathering data in the usual manner is impossible. But an expert believes that, when looking at the black holes through the concept of string theory, they become capable of taking on numerous shapes and size.

String theory does not operate with the known four dimensions, but with ten hypothetical ones. In this complex approach, black holes are apparently capable of looking like rings, helices, or even like the planet Saturn, expert Maria Rodriguez says. She is based in Germany, at the Max Planck Institute for Gravitational Physics, in Golm. The expert announces that she has just finished developing a catalog of all known class of black holes, and adds that string theory which is meant to be a unifying set of calculations that reunites Newtonian physics and quantum mechanics was very helpful in this regard.

Black holes are formed when massive stars that reach the end of their burning cycles expel the outer layers of their atmosphere in a violent supernova explosion. The remaining core then collapses on itself, due to massive gravitational attractions, and forms a singularity with an incredibly massive center. The gravitational pull that it exerts on surrounding matter is so tremendous that it forms an accretion disk around itself, and then begins to pull on normal matter from its surroundings. Even photons, which are the fastest-traveling particles in the Universe, cannot escape its pull, and fall through the event horizon.

According to Rodriguez, the only possible shape that black holes can take in four dimensions is spherical. But this is not the case when looking at it through string theory. In addition to compiling a list of all forms such a structure can exist in mathematically, the expert also proposes a series of conditions that these shapes must meet in order for them to become likely to exist in the actual Universe. Once verifying for compliance, we are still left with some very interesting objects, including blackfolds, black bowties, bicycling black rings, di-rings, and black helical rings."

==    == Our standard Black hole.. ===  == from astronomycafe ==

Like anything that rotates, it becomes flattened at the poles and broader at the equator. Here is a diagram showing the main parts of a Kerr, rotating black hole based on general relaticity:


Rotating 'Kerr-type' black holes become flattened, and their internal 'structure' changes in very interesting ways. In non-rotating black holes, the 'event horizon' and the 'surface of infinite gravitational redshift' is the same spherical surface surrounding a point singularity. For a rotating black hole, the event horizon detaches from the infinite redshift surface as you move from the poles to the equator where they have their maximum separation. The singularity becomes a ring in the equatorial plane of the black hole.

===

"Recently our understanding of black holes in D-space-time dimensions, as solutions of the Einstein equation, has advanced greatly. Besides the well established spherical black hole we have now explicitly found other species of topologies of the event horizons. Whether in asymptotically flat, AntideSitter or deSitter spaces, the different species are really non-unique when **. An example of this are the black rings. Another issue in higher dimensions that is not fully understood is the struggle for existence of regular black hole solutions. However, we managed to observe a selection rule for regular solutions of thin black rings: they have to be balanced i.e. in vacuum, a neutral asymptotically flat black ring incorporates a balance between the centrifugal repulsion and the tension. The equilibrium condition seems to be equivalent to the condition to guarantee regularity on the geometry of the black ring solution. We will review the tree of species of black holes and present new results on exotic black holes with charges. "

That means that although we expect them to be spherical if we ever could photo their event horizons / possible Hawing radiation, they in brane/string theory seem to be able to beget all kind of 'shapes'. Myself I'm particularly fascinated by the bicycling variant. I feel a certain kinship there :)
« Last Edit: 01/03/2011 16:03:33 by yor_on »
 

Offline graham.d

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What shape is a Black Hole?
« Reply #3 on: 01/03/2011 17:15:20 »
abacus, I think you are referring to the singularity at the centre of a BH and not the BH itself. A non-rotating BH in free space would be a perfect sphere, at least in most theories. I am unfamiliar with the discussions that yor_on refers to.
 

Offline Airthumbs

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What shape is a Black Hole?
« Reply #4 on: 11/04/2011 03:07:03 »
As usual I find the information given in response to my question very interesting.  Following about a month of reasearch into my own question I have to conclude that a Black hole is as graham.d states a perfect sphere.

Therefore the image I had previously, probably as a result of Stephen Hawkins & Hollywood, was incorrect.  This image of a Black hole being that of a disc, with a funnel leading down to a singularity, is misleading and I think confuses the way we think about these fascinating phenomenon.

Of course I am open to any other ideas that people might have and of course would like to know more.

 

Offline syhprum

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What shape is a Black Hole?
« Reply #5 on: 11/04/2011 08:10:19 »
To talk of the shape of an object one must define a surface this would normally be the event horizon in which case the shape would be spherical but somewhat flattened if rotating.
It is incorrect to say the density is infinite for large black holes it can be quite low.
A large black hole of 1 billion solar masses such as you would find in the centre of a galaxy would have a density of 32.7kg/m^3.
« Last Edit: 11/04/2011 08:36:28 by syhprum »
 

Offline JMLCarter

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What shape is a Black Hole?
« Reply #6 on: 11/04/2011 18:43:29 »
It is incorrect to say the density is infinite for large black holes it can be quite low.
A large black hole of 1 billion solar masses such as you would find in the centre of a galaxy would have a density of 32.7kg/m^3.

I don't think it is possible to know what the distribution of matter is inside a black hole. Equally there's no reason for the laws of physics to up and abandon matter at the event horizon, matter that falls in will probably continue to fall. This is indicative of a denser nucleus. How dense would it have to be for all matter to break down to energy - I think then it becomes a minimum size object... which is a size given by HUP?? So that would seem to not be infinitely dense per say, just graham's number dense (as my son would say [:X]). Is it a singularity then?

what about centripedefugal forces, could they prevent total collapse?

Anyway we are not talking about dividing the black hole mass by the volume delineated by the event horizon.
« Last Edit: 11/04/2011 18:51:09 by JMLCarter »
 

Offline kidbooks11

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What shape is a Black Hole?
« Reply #7 on: 11/04/2011 21:31:49 »
My theory is that it is circular. Everything seems to be circular so a black hole will be the same.
 

Offline peggy71

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Re: What shape is a Black Hole?
« Reply #8 on: 14/07/2013 19:01:26 »
The black hole at the center of the Milky Way galaxy is as large as the solar system. The black hole is a gravitational feature. That says to me it is influenced by the shape of our galaxy. It is well known to be a flattened disk. We casually think of a black hole as a one dimensional thing that objects fall into. But the strength of the  pull of the black hole is different depending on the configuration of the stars in the galaxy. It could change. Instead of the double stars getting caught by rotating too close, it could be the configuration of the black hole changes and one is in the way. How does the velocity or force of the black hole change depending on if you are in the area in the center in the front and the hole is round versus whether you are on the edge of the black hole, the outside edge of the disk? It seems that an object will go into it regardless of where it is and it will not go out the other side or into another universe. The black holes seem to change the forms of matter and the particles and spew some out. Instead of the black holes influencing the forms of the stars in the galaxy, maybe the arrangements of the stars influence the shape of the black hole and can change it. This would answer the question of why the early black hole in the universe after the big bang was so large, maybe it was reacting to having a lot more stars and matter closer to it back then.
 

Offline Pmb

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Re: What shape is a Black Hole?
« Reply #9 on: 17/07/2013 04:58:11 »
This might sound like an obvious question or maybe not.  A Black Hole, what shape is it in 3 dimensional space?
The black hole itself is the event horizon. The singularity itself is not the black hole but merely the gravitational source that is the source of gravity which creates the spacetime around the blackhole.
 

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Re: What shape is a Black Hole?
« Reply #9 on: 17/07/2013 04:58:11 »

 

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