I'm curious, I would expect most black holes in nature to be Kerr type. It's hard to imagine a black hole without spin since everything else (stars) seems to. Why did it take so long for them to find evidence for black holes? What was it about this one that made the frame grabbing noticeable? Was it very big or spinning quickly or something else?

Hi Roger,

Yep, most, if not all, should be of the Kerr type. It took until the early 1990s to confirm the first evidence of the existence of a black hole - they are by nature very elusive objects!

To observe the frame dragging is even more difficult, because the accretion disk (if one exists for the specific hole) is spinning at differential velocities (by distance) around the black hole. AFAIK, in the case under discussion, it was a very specific type of precession of the accretion disk that could only be explained by frame dragging. Accretion disks can precess due to other reasons as well...

After this first one, many other cases of frame dragging have been reported, some by other means, like the peri-apsis shift of a companion star orbiting the black hole at close quarters.

Regards, Jorrie

Hi Jorrie

The press release said "if our interpretations are right..."

Do you know if this has been confirmed? It is one thing to find a period or something that can be best described by frame dragging and quite another thing to prove it!

SL

Hi SL, you asked: "The press release said "if our interpretations are right..."

Do you know if this has been confirmed?"

I haven't got a reference readily at hand, but I feel quite comfortable that the 10 years of analysis and observations after that first one would have refuted the claims if they were not right!

Gravity Probe B has more or less confirmed frame dragging as a fact - still waiting for final results, though. But then, many other observations have also confirmed frame dragging!

Regards, Jorrie

Dear Jorrie:

...around non-spinning masses...

This is not a tease, seriously: Are there any non-spinning astro bodies? I was made to believe that any mass out there, even as a matter-cloud is imploding by gravity, starts to spin (or rotate), because of innate imperfection in it's symmetry planes. Isn't it so?

Regards, Yuval

Hi yuvalmate, you asked: "Are there any non-spinning astro bodies?"

I am not 100% sure, but generally, everything spins! Even if a contraction (or implosion, as you said) starts perfectly symmetric, a spin in some or other direction should result.

The only reason I can think of for a astro body not to spin relative to the universe at large, is in collisions or coalescence where the mean angular momentum cancelled out.

Regards, Jorrie

...mean angular momentum cancelled...

Are there any known such occurrences, or this is only permitted by theory?

Such occurrences could be, say, an exploded nebula which is at the resting-point between expanding and condensing?

Hi Yuval, you asked: "Are there any known such occurrences, or this is only permitted by theory?"

I'm not aware of any non-spinning compact structures that has been observed. It may also be that we have not detected the rotations of some compact structures (like black holes) yet.

In some very large structures, like galactic super-clusters, the overall spin may be so slow that it becomes undetectable.

But in theory it is possible for a black hole not to spin - if two identical black holes with precisely opposite spins coalesce to form one black hole, the new one could perhaps be rotation free.

Regards, Jorrie

...detected the rotations of some compact structures (like black holes)...

I understand black-holes are detected by the drag they pull on surrounding matter, and by a halo of x-rays emitted from their suspected coordinates, as they tear or stretch (differentially) the falling matter which heats-up as a result.

My question: can light-shift of x-rays be detected to hint Doppler-effect of rotation?

Hi Yuval, you asked "can light-shift of x-rays be detected to hint Doppler-effect of rotation?"

I don't think the Doppler shift can be used to determine the spin rate of the hole. The accretion disk is spinning at differential rates around any black hole, even if the hole itself is not spinning. As stated in the OP above, it is a characteristic precession of the accretion disk that was used to determine the spin rate of the hole.

Regards, Jorrie

Hi Jorrie,

The picture is worth a thousand words. I had not heard the term until your previous post, and was about to ask you if the frame dragged Aether with it, but matter - that's even better.

Jorrie,

Looking at the picture in your post, there's something funny. It appears that it is a space curvature picture (space-hyperspace diagram), somewhat like a ruptured trampoline, with the potential well of the black hole going down to infinity...

However, there are jets spewing out something along the spin axis in both directions. I can still buy it if the bottom jet represents matter being dragged into the central singularity, but the top one? It surely cannot spew something into hyperspace?

SL

Maybe photons excited and "guided" by surrounding electromagnetic field?

Hi Yuval

Not only photons, but also particles of matter guided by surrounding electromagnetic field...

As you probably know, the jets are not being spit out by the black hole, but come from just outside the horizon.

Jorrie

Hi SL, you wrote: "I can still buy it if the bottom jet represents matter being dragged into the central singularity, but the top one? It surely cannot spew something into hyperspace?"

Yep, I think the artist used a bit of artistic freedom there! Looks like he combined the hypothetical hyperspace dimension and the ordinary third space dimension for effect. Looks nice, but can be confusing.

The jets spew out into ordinary space and it would have been better if the curved space was not shown, just the dragging of the coordinate frame on a flat surface (which can be viewed as the projection of the curved space onto a flat surface).

Regards, Jorrie

I wrote: "In a future post I will attempt some quantitative data (calculations) on frame dragging..."

Due to work-related issues, I haven't hit the proverbial "sweet spot" with the "quantification" of frame dragging yet (the "sweet spot" would be the "engineering spin" on the topic).

So, please be patient and keep on watching this space...

Regards, Jorrie

Thanks Jorrie.

It is all still a mystery to me but it is a great mental puzzle to try and grasp. Keep the information pieces coming and I'm trying to build an understandable picture.

Jorrie,

Since space itself has energy-density and can itself exert a gravitational force, doesn't it stand to reason that rotating space would experience a centrifugal force?

What I mean is, wouldn't the frame-dragged space, say around a black hole, experience a slight asymmetry with respect to Hubble expansion, expanding slightly more in the direction perpendicular to the axis of rotation of the black hole and slightly less in the direction parallel to the spin axis.

Essentially I'm suggesting that space around any spinning mass expands outward in the direction perpendicular to the spin axis of the rotating mass due to some sort of spacial "centrifugal" effect. In this case I'm thinking of space as a substance like pancake batter being spread out by the spinning.

Could this account for the Pioneer Anomaly since expansion of space would slow the further away from the rotating body you got (thus increasing the apparent gravity)?

Hi Roger.

Firstly, a quick calculation to dispel any notion of the Pioneer anomaly caused by frame dragging. As I calculated in my Blog entry http://cr4.globalspec.com/blogentry/1670/Extreme-Frame-Dragging, the rate of frame dragging by the Sun at Earth's orbit is ω ≈ 7.16 x 10^-20 radians per second. The centrifugal effect caused by this rotation at a distance of r ≈ 1.5 x 10¹¹ m is around rω² ~ 10^-27 m/s². Further, ω itself falls off with the cube of distance, so it gets even more negligible farther out.

Now, closer to a black hole, the situation is obviously more severe, as I also calculated in the mentioned thread. I copied a schematic from it to the right. This black hole spins at the maximum possible rate. At the static limit, a free moving "static" particle will experience an apparent (Newton-like) centrifugal acceleration of ~ -5 x 10¹¹ g, due to frame dragging, which is balanced by the positive g's of the black hole's gravity. Since this particle is 'static' relative to the space around it (whatever that may mean), I suppose one can argue that the spinning space itself experiences this balance between centrifugal and gravitational forces.

However, I cannot figure how this can cause expanding space. In a sense, the space around non- or slowly rotating black holes is falling into the hole. I suppose at maximal rotation rate, the infall may be just checked, but expanding, nope, I don't think so...

-J

Hi Jorrie,

The calculations you have presented (very nicely) would be the effect of objects in space, not a hubble flow type effect as I am describing.

Again, I'm talking about an effect like Hubble Flow, not within the space. Essentially an asymmetric Hubble Flow like expansion. Yes the effect would be stronger closer to the sun and weaker further away which means if we take the force strength near the sun as "normal", the force away from the sun would appear "stronger" due to a weakening of the effect.

Quite frankly, I would find it astounding if rotating space, which has momentum and energy-density, didn't experience some kind of outward force on itself due to the spinning.

This outward hubble like flow, would be small compared to the hubble flow and appear as an asymmetry in the hubble flow.

I just did a quick search using the search phrase- spacial expansion due to frame dragging. I found the following article which I confess I can't tell if it is talking what I'm talking about or something else but it mentions the following in its abstract:

In Sect. 3 a zone of repulsive gravity is found in the extreme Kerr metric.

Here is a link to the abstract:

http://www.springerlink.com/content/w1481202165622t7/

Hi Roger,

I also had only time to scan the paper quickly, but it looks like he separates the Kerr metric (spinning black holes) from cosmological 'frame dragging" completely. I somewhat think that way as well.

Sure, there is an effect like radial dragging of inertial frames in an expanding universe, versus the transverse (rotational) frame dragging near spinning black holes. I have written on the cosmological effect in my Blog on Particle momentum decay. I never viewed it as dragging of inertial frames, but I suppose it is a valid view. Nevertheless, I still do not think spinning black holes have anything to do with cosmic expansion...

-J

Hi Jorrie,

I feel like I'm not being clear about this. Although I do expect there to be radial dragging of inertial frames in an expanding universe, that is not what I'm talking about here.

Let me try this approach of explaining my idea.

Lets say space is like a fluid. If you stir a fluid it spreads out (centrifugal force). Frame dragging is like stirring the fluid of space, so what i'm saying is I'm expecting it to spread out (expand outward) as a result.

I expect this to be a tiny effect because of the small energy-density of space, but still I expect the effect to exist.

Hi Roger,

Yep, you may well be right, but then the question comes up: how can we detect that?

Only by studying the movement of particles. The orbital equations for Kerr black holes are complex, but known. They are not directly solvable, but numerical calculations can be done. The geodesics of particles around Kerr holes may include such an effect (particles take longer to fall in), which you could call "expanding of local space" if you like.

Similarly, 'expanding space' in cosmology is only observed as inter-cluster distances that increase over time. But, do remember that vacuum energy density remains constant - it does not 'thin out' out in an expansion cosmos, or 'get denser' in a contracting cosmos.

-J

I agree and understand, especially the last statement.

I also have been wondering if an electron's intrinsic spin causes frame dragging.

A side note for the "Physics Forum Guru's"

Now, before some grad student from "physics forum" starts telling me that an electron is a point particle and intrinsic spin isn't regular spin and so frame dragging wouldn't apply to that type of spin, let me preemptively disabuse them of their mistaken confidence (nothing like a grad student with a little knowledge...)

First of all there is no such thing as a "point particle" due to the uncertainty principle. Secondly, that "intrinsic spin" that isn't "spin" produces a magnetic moment and angular momentum and a whole host of classical spin effects in the quantum regime. So it may not be "classical spin", but it sure does classical spin like things in a quantum mechanical way. So there really is no reason whatsoever that an electron doesn't frame drag too as far as I can see.

That said, and electron effectively would be spinning pretty fast (to produce it's measured moment) but it is very light.

Back to my question

So my question is, has anyone seen anything on frame-dragging around electrons or other particles? I know the effect would be tiny (to say the least), but the scale would also be small, these effects would only have to be measurable at very short distances to effect a spectra.

Hi Roger, I know too little about quantum physics to answer, but I haven't heard of any measurement like that.

To me it sounds a bit far-fetched (even the Earth's frame dragging is extremely hard to measure), but one never knows.

-J

Hi Jorrie,

I finally had some time to look around and found the following paper. I'll send the full thing to you, in the meanwhile, here is the abstract:

http://prd.aps.org/abstract/PRD/v81/i2/e024027

Roger