A Kinked Link, Aug 1, 2011

[jjohnson]

Take a good look at the last 3 paragraphs in this TPOD. This part starts to get at the heart of the matter - what makes these things happen in space? The TPOD states,"Toroidal filaments couple to hourglass-shaped current sheets that are subject to diocotron instabilities...", and the included link, "forms vortices", links to a Very-long-baseline radio telescope image with superimposed twisted lines purporting to show the helical vortices discovered in the jet from galaxy 3c273. What are these vortices, and under what conditions do they form, and how do we know?

This is a cautionary lesson on practical skepticism.

My first thought was, "looks like two parallel Birkeland current filaments undergoing normal Lorentz attraction, winding in around each other until opposing forces overcome the attraction and stabilize their distance apart." Then I read the article from which the image was taken (by right-clicking the blue link, selecting Copy Link Address, pasting it into my browser's new window, and deleting the image portion [ /fig_model.gif ] at the end of the link address). This brings up the actual article from the Max Planck Institute, which tells a lot more about the work on this jet.

The article stated that "The MPIfR scientists have shown that this double helical structure is consistent with Kelvin-Helmholtz (K-H) instability developing in a light jet with Lorentz factor of 2 and Mach number of 3.5." I brought that up with Steve Smith, who noted back that, "Tony Peratt told me that it's often tempting to use fluid dynamics to explain plasma but don't do it." Luckily, Steve's wise words set me to thinking, and I got the article back up, and got out Peratt's book to see precisely what he did say. (Measure twice; cut once.)

The Max Planck Institute article says

Studying the origin and development of plasma instability in extragalactic jets is crucial for understanding the nature of relativistic outflows from AGN. K-H instability is the most likely type of instability to be found in extragalactic jets... Recent theoretical works have predicted that K-H instability should produce complex, three-dimensional ribbonlike and threadlike patterns inside a relativistic jet.

They also say that, "To determine the interior structure of the jet, the MPIfR researchers have obtained and analyzed 240 profiles of brightness distribution across the jet. In most of the profiles, the presence of at least two distinct features is visible." You can download and see the step by step cross sections as the imaging line is moved along the jet. Only a few of the images look to have two discrete peaks, and one is usually almost buried in noise.

So, the article is theoretical, it uses MHD which leads to the fluid dynamics K-H instability, against the advice in Hannes Alfvén's Nobel Address, and it depends on a perturbation-based model to winkel out the helical flows:

To explain the presence of such a peculiar pattern in the jet, the MPIfR researchers have applied linear perturbation analysis of K-H instability, and successfully modelled the observed structure of the jet. Their model explains in detail the internal structure of the jet on scales of up to 30 milliarcseconds (~ 300 parsecs).

20 years ago, Peratt writes in his Physics of the Plasma Universe, Springer Verlag, 1992, on p.29, 17.3 The Diocotron Instability:

One of the outstanding problems in the propagation of electron beams along an axial magnetic field is the breakup of the beam into discrete vortex-like current bundles when a threshold determined by either the beam current or distance of propagation is surpassed. The phenomenon observed closely resembles that associated with the Kelvin-Helmholtz fluid dynamical shear instability, in which vortices develop throughout a fluid when a critical velocity in the fluid is exceeded, with a large increase in the resistance to flow (Chandrasekhar, 1961).

Since a galactic jet is an axially aligned plasma current and not a fluid, the Max Plank scientists did not use "best available science 20 years ago" to interpret their beautiful data, but instead used precisely the method that the inventor of magnetohydrodynamics MHD himself developed and warned them will not yield behavioral models that conform to reality and observation.

The link in the TPOD to aurora studies is also borne out by Peratt on p.30:

...in the laboratory, well-defined vortices are found to occur over 12 orders of magnitude in beam current. This mechanism [diocotron instability] was first introduced to explain auroral curtains (Figure 1.21) by Alfvén (1950). The diocotron instability is discussed [further] in Section 2.9.8.

So be very careful in checking your background references for plasma phenomena whenever you read even the best-looking papers from the most prestigious institutions, because still today they very well may still be unaware of the straightforward experiments and resultant expert advice offered back in the day, and may simply proceed with their MHD theoretical models and mathematical sophistries to generate images that reinforce what they think they are looking for.

The recent excellent paper, "Measurement of the Electric Current in a kPC-scale Jet", arXiv:1106.1397v1, 7 Jun 2011, has as 2 of its 4 authors Phillip Kronberg and S.A. Colgate of the Los Alamos National Laboratory, Sandia, New Mexico. These guys know astrophysics and electrodynamics, and they don't mince words like electric current when that is what they are setting out to measure and describe. Peratt is also associated with Los Alamos Labs, and I bet dollars to donuts that they have well-thumbed copies of Peratt's textbook in their library!

Jim

[flyingcloud]

quite right, thanks for this illustration Jim. nice example

[jjohnson]

Thanks; see today's TPOD (Cloudy With a Chance of Instabilities) for another take.

There is a great deal of pattern-matching going on in our brain as it processes sensory information. This is simple Survival 101. In fact, what we think we see is so heavily pre-processed at an unconscious level before we become aware of it that sometimes we actually do not see information that the brain has processed and discarded as "not suitable for prime time in the Conscious right now".

One form of pattern-matching is called similitude. Things that look alike at first glance may be assumed to be alike, to work alike, to behave alike, to take similar descriptors and respond to similar "models". There are exceptions, as the on-going discussion illustrates when comparing complex plasma behavior, which is generally governed most strongly be electromagnetic forces, to fluid behavior which can be governed directly and indirectly by gravity and magnetic fields (MHD) in cool, condensed matter.

But if an observer (astronomers come to mind here) is knowingly watching material or a phenomenon in which the temperature or other ambient energy field is high enough to ionize neutral matter, even a small fraction of it, her interpretation of it needs to turn to electrodynamics and plasma physics, not fluid dynamics. This should be taught in school as soon as students are taught in science class that there are 4 basic states of matter, the first of which is plasma. It has not been, to the general detriment of the advance of astrophysics.

Incidentally, lest anyone think that I am saying that the Max Planck Institute's authors did not really observe twisting filamentary currents - they did, and they called that right. But what was wrong is that they built their model upon and used classical MHD phenomena to try to explain a plasma phenomenon. That was the error.

Jim

[flyingcloud]

it's been difficult for me to make the transition and accept the difference, I find myself "gravitating" toward (MHD) instinctually, I force the issue when I catch it now, it was a broad leap, thanks again, keep up the good work

[Jarvamundo]

Thanks Jim,

After reading Kronbergs paper, i went back and read through the evolution of Alfven's ideas of scaling his lab circuit, to the auroral circuit, to the solar circuit, and then so again to the galactic circuit. For which Alfven arrives at a scaled value for the current of 10^17 amps [see fig 4], and makes a brief quantitative comment of an expectation of an order of magnitude difference [see discussion on quantitative considerations end of paper].
http://adsabs.harvard.edu/abs/1978Ap%26SS..54..279A

Kronbergs measurements (10^18A) put Alfven's extrapolations well in the ball park... he kinda nailed it there. Pretty neat how the empirically derived scaling laws from lab and magnetosphere-circuit probes, and essentially the same circuit layout can be applied, to make these predictions.

But it doesn't stop there, Alfven is also adamant in this paper about discussing the role of the electro-static double-layers appearing (generally) axially to the homopolar. Drawing these as capacitors in the circuit; for the auroral circuit, for the heliospheric circuit and for the galactic circuit. It's the same circuit setup, with scale factors. as per Discussion:

The circuit consists of an emf, a resistance, an inductance, and electrostatic double layers. The difference between the four cases it is applied to, is essentially geometeric.

Alfven also stresses the importance (in his proposed model) of the 'accelerating double layer' located 'at the tips' of the pinched axial current.

Figure 4(b) shoes the radio astronomy picture of a double radio source. It is essential in our model that the emf of the galaxy has such a direction that the axial currents flow outwards. The double layer they produce should be located at the outer edges of the strong radio sources. When the electrons conducting the currents outside the double layer reach the double layer, they are accelerated to very high energies.
....
....
It should be stressed again that, just as in the magnetosphere and in the laboratory, the energy released in the double layer is transferred to it by electric currents which essentially consist of relatively low energy particles. There is no need for a beam of high energy particles to be shot out from the central galaxy (and still less for some mysterious plasmons). On the contrary, the central galaxy may be bombarded by high energy electrons which have obtained their energy from the double layer.

The importance of the axially located double layer at the end of the pinch, is stressed over and over again. The "great accelerator" is awaiting particles as a result of the established circuit. The ridiculous velocity wooshy jets are simply not needed. The natural process that exists in the lab, in the auroral circuits is waiting to speed any particle of charge.

Beautiful.

Ofcourse, it doesn't stop there... The great polar accelerators [axially positioned double layers] are also able to accelerate and emit ions of an energy of cosmic rays. So completely inverse to 'windy pufffy smokey jetty' you will have a near invisible accelerator that 'appears' axially above and below. The 'caps' sitting on the radio lobe's tips will accelerate cosmic rays... and ofcourse we read recently from Wal's "Alfven Triumphs"..... those accelerators >are< there, doing their 'thang right here in our solar circuit.

http://www.holoscience.com/news.php?article=4eefp0kj

Alfvén’s Solar Circuit Confirmed
On May 3, the New Scientist published an important article by Anil Ananthaswamy, “Strange cosmic ray hotspots stalk southern skies.”

Cosmic rays crashing into the Earth over the South Pole appear to be coming from particular locations, rather than being distributed uniformly across the sky. Similar cosmic ray "hotspots" have been seen in the northern skies too, yet we know of no source close enough to produce this pattern.

Same circuit.

Double layers sitting in their place... doing their thang.

Over and over again in Alfven's writing he repeats "double layer" "double layer" "double layer". I'm come to find, that this >is< the key to understanding the natural circuit. Look for where they are positioned and what they do. From here you will find the qualitative death blows to jet descriptions. The circuit means there is just no need for puff. It's a completely different view. This is 'the message' of Alfven.

If you ignore the existence and natural position of these 'great accelerators' in the circuit... you're toast.

Krongberg is running oncourse to encounter this.

The system evidently needs to have a “transducer” that
converts the Poynting energy flux into high energy par-
ticles which then produce synchrotron radiation.

Alfven's accelerators are awaiting on 'the tip of the lobes'.

The more i absorb PC, the more fractal nature of this same circuit sinks in, a repetition of the same circuit, a simple repetition of natures energy transfer system. Nature gives us a lesson on how things slow down, and how things speed up. Which (if the universe is evolutionary and infinite) you would plainly expect to see all systems develop like this. This is where the big bang limits your awareness... you expect explosive, jetty, expansitory death... thus becoming awareness-poor of natural cycles of re-cycles. You just don't expect to have a giant capacitor sitting out axially above your body, accelerating things.

"Same circuit, different scale" is the message... all the same circuit elements will be there, doing their thang.

neat.

forget the fluids, see the circuit, grab a beer, sit back and let the evidence do the rest.

/just another day in the plane of a homopolar.