Black holes representations

[Run Duke]

Hi, black holes are always represented like "water" swirls in space but since their enormous gravitationnal forces are effective in all directions what would be their true representation?

[Dr. Skeptic]

http://antwrp.gsfc.nasa.gov/apod/image/ ... n_full.jpg

This is our best guess.

Because of rotation, magnetic fields, etc. the incoming material will always form an accretion disk as close to a stable/uniform orbit as possible. Any material that does not match the orbit of the accretion disk will be subjected to high velocity impacts ejecting it away from the BH or be assimilated. If two accretion disk attempted to form, the energy and the mass of the two would " average-out" to create one disk.

Polar jets are not depicted on this computer rendering and is not true color but base on a temperature scale.

As you can see it does resemble H2O exiting a drain.

[BMAONE23]

Two disks might be stable for a long while though, there was that image of a double disk around a star a while back. (granted, a star's gravitational pull and disk rotational speed is vastly different than that of a Black Hole)

[Run Duke]

Well, "like water swirls representations" are caused mainly by rotation... so first question:
Neutron stars rotate often at very high speed...so at what speed do black holes (or the singularity within) turn?
Second:Does the possibility of a non-turning black hole exist?

[iamlucky13]

Keep in mind this all theoretical (it works on paper, but it hasn't been directly observed):

Black hole spin is determined by conservation of momentum. Since any matter accreting onto a black hole (or a star that will later go on to form a black hole) is likely to have some angular velocity relative to a black hole, that momentum is absorbed with the matter. Unless a given unit of matter happens to have an initial velocity straight at the black hole and there are no disturbances, you can bet that it will carry some angular momentum into it.

So to approach both questions at once they should spin, but they don't fundamentally have to. As for the speed, I don't know the answer to that, but consider a figure skater doing a spin. Because of the conservation of momentum, if she pulls her arms towards her, her spin increases. A black hole has essentially pulled all of its mass within its event horizon, so it should spin quite fast...

However, Roger Penrose has shown that some relativistic effects of the spinning can actually cause energy to be transferred from the black hole to objects near, but not inside its event horizon, slowing the hole down over time.

Here's a decent article with some more details:
http://en.wikipedia.org/wiki/Rotating_black_hole

In short, a non-spinning black hole should be possible, but incredibly improbable.

[Dr. Skeptic]

Let me clarify myself, the accretion disk (when present) will always spin and the rotation will eventually be orientated to any rotation the BH may have.

http://antwrp.gsfc.nasa.gov/apod/ap011029.html

[Run Duke]

http://heasarc.gsfc.nasa.gov/docs/objec ... ng_bh.html

So it seems that the possibility of spinning and non-spinning black holes exist. What interest me is to imagine the structure of the gravitional fields these two kind of objects would have if represented as if it was a magnetic force field. In the case of a non spinning black hole would this take the form of a sphere?

[Dr. Skeptic]

A sphere is out of the question. The accretion disk is a product of its rotational speed of the material and the pull of gravity. When the particles are not in a unified orbit, the rate of collisions increase proportionally to the difference in angular momentum, robbing the some of the particles of their speed causing them to be assimilated by the BH, and increasing the speed of others allowing them to escape the BH's orbit, thus leaving a stable orbital plain. An accretion disk will have the fewest amount of collisions = most stable.

A sphere of material enshrouding a BH would quickly derogate into a single accretion disk following the most efficient orbital path around the BH. The presents of a rotation and/or a magnetic field determines the path of the most efficient orbit.

[Qev]

Personally, I'm not certain how the 'shape' of the gravitational field would differ between a rotating and non-rotating black hole, however I do know of one significant difference: rotating black holes possess an 'ergosphere', while a non-rotating black hole would not.

The ergosphere is defined as that region around a black hole, outside of the event horizon, where no possible orbit is stable. In other words, the orbital velocity required to maintain a stable orbit exceeds the speed of light. This effect occurs due to 'frame dragging', the rotating mass of the black hole actually dragging spacetime itself around in a circle. The ergosphere reaches a maximum diameter along the 'equator' of the black hole, and a minimum diameter (coinciding with the diameter of the event horizon) on the polar axis... basically a squashed sphere.

Non-rotating black holes more than likely don't exist, since pretty much everything in the universe that could form a black hole is already rotating. Even if one were to form, it would soon enough start picking up angular momentum from material that it consumes.

[ta152h0]

One assumes rotation but how can a singularity be rotated ? as time is an added dimension, we don't have proof the black hole ( a mathematical solution ) is located at the center of the observed rotating material ? just being a devil and pass the ice cold one !

[Dr. Skeptic]

More proof that singularities don't exist.

[ta152h0]

it is not possible to observe a singularity, only the effects. I cannot comprehend the concept of a singularity, anymore than I can comprehend the square root of a negative. Doesn't necessarily mean either one doesn't exist. 8)

[iamlucky13]

One assumes rotation but how can a singularity be rotated ? as time is an added dimension, we don't have proof the black hole ( a mathematical solution ) is located at the center of the observed rotating material ? just being a devil and pass the ice cold one !

There does not have to be a singularity at the center of a black hole. A black hole just needs an event horizon, but if the mass is high enough, it seems it might also be possible to contain a singularity.

So this mass, although extremely dense, is not infinitely constricted. It has a radius and therefore angular motion theoretically has meaning.

I don't even know where to begin accounting for angular momentum in a singularity.

The wikipedia article I linked to above claims that an extremely fast spinning black hole may actually have its event horizon collapse down to nothing, leaving a "naked singularity." I'm a more than a little skeptical about that one.

[ta152h0]

I am just a regular guy who knows a lot of stuff, as opposed to scientists who can prove a lot of stuff. It is impossible to describe black hole geometry in cartesian coordinates and because time is an added coordinate, we are destined never to observe a black hole, only its effects because the bloomin' thing acts as if it has a great mass concentration. I believe a blach hole has a very short life and it is related directly to gamma rays ( or even other rays we are not able to detect yet ) .

[ckam]

It is impossible to describe black hole geometry in cartesian coordinates

It is actually good that you mentioned that, since when I hear people arguing about things like ergosphere and such, I only think to myself "wtf are you talking about". Every form of BH metric I have seen is written in coordinates that have very little to do with times and distances as we know them, and it is very inobvious how phenomenons like singularities and ergospheres translate from those coordinates to what laymen call "space and time"

[iamlucky13]

Well, "like water swirls representations" are caused mainly by rotation... so first question:
Neutron stars rotate often at very high speed...so at what speed do black holes (or the singularity within) turn?
Second:Does the possibility of a non-turning black hole exist?

I saw anarticle today that prompted me to revive this thread briefly.

Some researchers have indirectly measured the rate of spin of three black holes. The fastest is making 950 revolutions per second. Based on its mass, it has a theoretical maximum spin rate of 1150 rps. I believe the maximum is limited by the event horizon approaching the speed of light.

The paper concludes that GRS 1915 and two other black holes studied by the team were born with their high spins. That is, the collapsing core of the original massive star poured its angular momentum down into the black hole.

[orin stepanek]

I don't know whether this is helpful or not but here is some interesting stuff on black holes. 8)
http://casa.colorado.edu/~ajsh/schw.shtml
Orin

[harry]

Hello Orin

Thank you for the link

Always reading

[harry]

Hello Orin

Had a look at the link

http://casa.colorado.edu/~ajsh/schw.shtml

nice images
http://www.cv.nrao.edu/~abridle/images.htm

and more

Good on you Orin, nice link