In the Solar Wind as an electric current thread, here in ATM, czeslaw wrote thus:So I started this thread to discuss his idea.

Perhaps a good place to start would be to briefly describe the several states of the ISM (interstellar medium)? From the dense (funny adjective, it'd be an excellent vacuum here on Earth) core of a giant molecular cloud, to the rarified, high temperature environs of an SNR (supernova remnant - the bits 'inside' the shock front), and maybe on to the IGM (inter-galactic medium)?

Thank you Nereid.
I am fascinating of the galaxy structure. A galaxy has so many stars like the atoms in a living cell .

There is a nucleus in the galaxy and the globular clusters like the mitochondria in a fluid of halo. The dense nucleus with blach hole, neutron stars, magnetars , supernovae, dispose of the matter and energy in the galaxy. The new stars are born in the nucleus and arms and then are dismissed into halo. Everything is controlled by currents in the plasma and held in a balance.

How? By what mechanism?

The strongest force seems to be a gravity but that is not all.
Something protect that a mass do not collapse in one Black Hole and the currents of a matter perpendicular to the galaxy plain are possible.

Very thin and rare gasoeous plasma of charged particles is about 20 % of the whole galactic mass. AGN , magnetars, supernovae create strong magnetic fields, send Cosmic Rays.

There are Birkeland electric currents, magnetic fields, double layers in plasma, electrostatic interactions.

The galaxy is much more complicated the our living cell without gravity.

How do you know?

Where are they?

What are their characteristics (strengths, directions, etc)?

How are these determined?

Of course, I'm referring to the Milky Way ISM (not the solar system IPM, or Earth's magnetosphere, or ...).

Excuse me, but you have to check up on your astronomy, the stars in the halo, i.e. in the globular clusters are of the oldest generation in our galaxy.
I will refrain here from the currents and plasma, because that discussion will definitely start in the next message.

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善數, 不用籌策 (shàn shù, bù yòng chóu cè)
He who is good at counting, uses no counting tools
“A good scientist has freed himself of concepts and keeps his mind open to what is”
道德經, 二十七 (dào dé jīng, 27)

As far as I know in the galaxy halo are the oldest stars and they are mostly in a globular clusters. There are over hundred GC in our galaxy halo. It is amazing how galaxy dismiss used matter.

Magnetic field of the Milky Way is about 10^-10 T, it is a galactic electric current about 10^17 A. Such a magnetic field can’t alone to keep a star but can keep Cosmic Rays and hydrogen clouds.

Galaxy is embedded in a massive sea of hot intergalactic gas. For example High Velocity Clouds (HVC) with mass about 100 mln solar masses fall towards galactic disc. They brings about 0,2 solar masses/year.

There are the currents of matter – Sagittarius current and Magellanic current. There are many intergalactic currents passing through plasma in pairs often and they may compress any material between them and accrete (Marklund convection).

Around our Orion arm is an Orion’s veil consists of several layers of neutral gas and ionising stars producing layers of high ionised gas. This arm is an independent system where stars are held by gravity and as whole with many double layers move under pressure of the halo plasma and the gravity of the galaxy bulge .

That is what I said! so if you agree it does not make sense to say that the start get born in the nucleus and then are dismissed into the halo. Do you have any idea how much energy that would take? But we disgress already here, we are talking about currents in the ISM

care to enlighten us here, how do you calculate the current, how do you expect the field to keep the cosmic rays?

Okay we have to make some definitions here, otherwise we get majorly confabulated, there are ELECTRIC CURRENTS and there are MATTER FLOWS, let's NOT call the matter flows currents (as in the analog with the ocean).

And then, Birkeland currents are something special, actually, they are defined for the Earth's magnetosphere only.

Czeslaw, you seem to think that cosmic rays are something magical, the Gandalfs under the high energetic particles. Why?

you may want to put some physics here, how e.g. double layers will hold stars in their place, or whatever you mean here.

For the rest I join Nereid with his questions.

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善數, 不用籌策 (shàn shù, bù yòng chóu cè)
He who is good at counting, uses no counting tools
“A good scientist has freed himself of concepts and keeps his mind open to what is”
道德經, 二十七 (dào dé jīng, 27)

Hannes Alfvén and Carl-Gunnar Fälthammar say in their book, Cosmical Electrodynamics (2nd ed. 1963):

"Since cosmical clouds of ionized gas (plasma) are generally magnetized, their motion produces induced electric fields according to the formula (3) . These induced electric fields are of great importance in many astrophysical problems.."

So, the questions then becomes:

1. Is the Interstellar Medium (ISM) a plasma?
2. Is the ISM plasma moving?
3. Is the ISM magnetised?

If the answer to these questions is yes, then there is an induced electric field, and hence a current. Of course that still begs your original question, but we also know that the movement of the Interplanetary Medium (Solar Wind plasma) through the Sun's magnetic field produces one of the largest structures in the Solar System, the Heliospheric Current Sheet.

Regards,
Ian Tresman

It may be that we will need to get into at least OOM quantification soon, to avoid pages and pages of words that read pretty but are basically empty.

Let's see:1. In the post which began this thread, I suggested that we look at the several states (a.k.a. phases) of the ISM; from here:

Coronal Gas: T >~3x10^5K, n ~0.003 cm^-3, f ~0.4

HII: T ~10^4K, n ~0.3-10^4 cm^-3, f ~0.1

HI Warm: T ~6000K, nH ~0.3 cm^-3, f ~0.5

HI Cool: T ~100K, nH ~20 cm^-3, f ~0.02

Diffuse H2: T ~60K, nH ~20-100 cm^-3, f ~0.01

Dense H2: T ~10-100K, nH ~100-10^6 cm^-3, f ~0.0005

where T is the temperature, n(H) is the space density of constituent particles (H), and f is the fraction of the volume of the (Milky Way) galaxy composed of that phase.

Perhaps, Ian, you can tell us which of these phases is a plasma?

2. "Motion" is quite tricky; of course the constituent particles are 'moving' (after all, they are not at 0K!), and Alfvén and Fälthammar certainly didn't mean this kind of 'motion'.

So, what kind of 'motion' did they mean Ian?

3. How can you tell? More importantly, though your question was worded as an absolute (it's either 'magnetised' or not, and even a magnetic field of 10^-999 T would be 'magnetised'), surely a much more important question would be "at what magnetic field strength would the kinds of effects Alfvén and Fälthammar mention become non-trivial, for the various types of ISM plasma?"

Care to take a stab at answering this Ian?Let me give you another question to which the answer is YES, to illustrate why playing with words alone isn't helpful.

We all know about 'tunneling', don't we? How electrons (for example) can 'tunnel' through a potential barrier that, under classical physics, would be impossible for them to do so (this is the basis of those marvellous 'tunneling microscopes). IOW, it's a real effect, and the size of the effect can be calculated from quantum theory.

Suppose I ask, analogously to Ian's question: "Can Nereid 'tunnel' from Nereid to Io?" The answer must be YES.

But of course Nereid would be exceedingly foolish to consider this as means of transportation, even if Nereid were to live for 999 trillion years.

So, how big would such induced electric fields, and currents, be? How important would they be in terms of producing effects that made a difference (in any sense you care to name)?

In galaxy halo are the very old (perhaps the oldest) stars and we do not observe new stars. Why ? There is a plasma like in every star. The problem is that stars are born if there is proper relation between neutral and ionised hydrogen. A plasma can’t collapse into star. The galaxy halo is almost plasma and the stars in the halo have came from a galaxy disc or nucleus.

I do not know how a galactic magnetic field keeps the Cosmic Rays but it is written in every astronomy links – The Cosmic Rays move in the galaxy more then 10^7 years.

O.K. There is a Sagittarius and Magellanic matter flow with an unknown electric current.

The Cosmic Rays seems to me something special.
A source like AGN, magnetar or supernova ejects charged protons and electrons very fast according to energy of the magnetic field. The electrons are not joint to the protons and if they have less mass, they move faster having the same energy like the protons. The electrons interact with photons and fields and lose their energy. The protons remain very fast.
When we observe the Cosmic Rays at the Earth , there are almost high energetic protons only. The Cosmic Rays are very rare but they should pull the electrons to balance a local charge. I do not understand it exactly.

The plasma can’t holds a star but a galactic arm behave like an independent cloud of stars and gas joint by the gravity. This cloud is some thousand light year of diameter and much more longer. The average density of such an arm is not high. This arm like a cloud is pulled by a galactic mass , magnetic field and press by the halo plasma.

Aren't we just trying to ascertain whether the interstellar medium (ISM) includes matter in the plasma state? Ultimately, it is surely just a yes/no answer, though I can see that we are still trying to define whether it is a plasma.

I admit that I don't know enough detail to determine whether the areas you mention are plasmas, though Coronal "Gas" and HII seem likely. I don't knw about the others, but as you may have read, if they are partially ionized, then they still count as plasmas (a bit like mixing enough water with soil, and the resulting mudslide flows like liquid). So even the partially ionized HI regions I suspect are plasmas too. That leaves the diffuse and dense hydrogen regions, who state will depend on the degree of ionization.

Nevertheless, it does seem that at least some of the interstellar medium is indeed characterised as being in the plasma state, and there are peer reviewed papers which may provide additional information.

Indeed, not least because electric and magnetic fields require a coordinate frame of reference. All I can say is that I have not found any references that suggest that the interstellar medium is stationary.

I agree, and perhaps this is the reason for your order of magnitude questions. I would be a little simplistic to suggest that it doesn't matter. For example, if we identify a substance as being in the liquid state, then by definition we know some of its characteristics. And just as the force of gravity is insignificant on some scales, it may not be on longer time scales. Likewise plasma. The interplanetary medium may be at very low pressure, and the effect of the Sun's magnetic field small at the Earth's orbit, yet the heliospheric current sheet is the resulting structure that is perhaps the diamter of the Solar System.

But we can estimate how plasmas will behave in the interstellar medium by looking at plasma scaling laws as applied to their scale, density, magnetic field, and 'characteristic time'.

So the answer is that the diffuse plasma in the interstellar medioum does still behave as described by Alfvén and Fälthammar, but obviously more slowly and on large scales.

Regards,
Ian Tresman

This plasma scaling laws are very interesting, Ian,
What is possible for a short moment in a laboratory may work as a stable system on the galactic scale.

There you go again Ian, 'stationary' is another absolute!

So the same question applies: what 'motion' is required before the effects become non-trivial?Thank you for the link.

As we can all immediately see, scaling from a lab plasma to the ISM won't work - it is already well-known that atoms (ionised or not) in a magnetic field of 10^16 G behave quite differently than ones in a field of 10^-5 G (even light behaves differently) ... at least not a lab plasma with a characteristic length of 10 cm! It is also important to bring readers' attention to this sentence on that webpage: "Alfvén and Fälthammar note that while the similarity transformations are useful for some basic properties of plasma, they do not necessarily work for other. For example, hydrodynamic waves do not obey the transformation."

Conclusion? We can't 'estimate how plasmas will behave in the interstellar medium by looking [only] at plasma scaling laws'.

So the answer is that the diffuse plasma in the interstellar medium does NOT behave as described by Alfvén and Fälthammar (at least, not per Ian's initial reference)! #-o Indeed. Then again, maybe not (see above).

So, since this is a thread in ATM, how about we have czeslaw (or Ian) make a claim? Propose a 'theory'? concerning electric currents in the ISM, of course.

Then we can challenge it.

I interpretted it slightly differently, that the plasma scaling laws may work for certain basic plasma properties, but may not work SPECIFICALLY for hydrodynamic waves (which does not exclude other properties).

I took the conclusion to mean that there may be some basic properties of plasmas that do scale.

I have some more information that I can provide you with, if you email me. I have sent you a private message.

Regards,
Ian Tresman

Perhaps it would be a worthwhile investment of your time, Ian, to become more familiar with the ISM?

I mean, it's going to be very difficult for you to defend whatever 'electric current in the ISM' ideas you (or czeslaw) put forward (this is the ATM section of BA) if you are as ignorant of the basic aspects of plasma physics and of the observational results concerning the ISM as your posts in this thread indicate (to me, at least).

There is an average magnetic field in our Milky Way about 10^-10 T. It is obvious , that there is an electric current too. The question is , what this current can do and what phenomenon are additionally connected with it.

We can compare our galaxy to the our Solar System, I think. That way an electric current might move in the galaxy as well as in an interplanetary current sheet it moves. We observe the clouds of hydrogen moving from the galaxy centre and High Velocity Clouds (HVCs) falling down to the galaxy plain. It may indicate a direction of some forces, I think.

Indeed.

Perhaps we could start with an estimate of its strength?

However, there's also the question of the nature of this current, if the Milky Way's magnetic field isn't uniform (which it isn't).All this may be so.

However, unless and until we see something more than handwaving, I'm sure you'll agree that we don't have enough to even start a discussion, do we? #-o

Can we see something more than handwaving, please?

Neirid, I have offered you on at least six occassions, via private messages, to contact me by email for some more detailed information, that includes the maths I think you are looking for.

I'm beginning to think that you won't look through Galileo's telescope :-)

Regards,
Ian Tresman

Ian
I would say, just put it here, so we can look at it, you may mail it to me (tusenfem@yahoo.com) and I can take a look at it.
Unfortunately, well for you all, not for me, I go on vacation next week.

I also think we should be careful to use wikipedia as a source for info. A lot of stuff in there is probably okay, but I put more trust in books.

Also the scaling laws for plasmas we have to be careful with, how to interprete these scalings and which scalings we can use. E.g. to go to the lab frame and have to increase the magnetic field by a huge factor changes the whole phyiscs. In interstellar space the particles may be weakly magnetized, if you then go to the lab and increase B with something like 10^5 or so, it is no longer the same problem you are looking at.

yes, and the force is gravity for neutral hydrogen clouds and the force is as expected towards the central plane of the galaxy.

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Any comments in glorious red are to be considered in ModeratorMode.


善數, 不用籌策 (shàn shù, bù yòng chóu cè)
He who is good at counting, uses no counting tools
“A good scientist has freed himself of concepts and keeps his mind open to what is”
道德經, 二十七 (dào dé jīng, 27)

Yes, it could be hand waving but in right direction, I think.
A principle is when something is theoretically possible, then it is real too.

I have one not solved problem with a Cosmic Rays. The protons and electrons are accelerated in a magnetic field of AGN, magnetar or supernova and reach a velocity according to the received energy. The electrons interact with Background and thermal photons and lose its energy. That way we do not observe high energy electrons in the CRs on the Earth. There are almost protons or nuclei only. This charged protons will pull the electrons and cause an electric current. How are this fast protons balanced if the electrons are slower?

Apologies Ian, I think there's a communication breakdown.

If I had wanted this material just for myself, I would have sent you a PM (or availed myself of the excellent services of Ms/Dr Google).

That I ask for clarification/amplification/etc here, in ATM@BA, means I am expecting a public reply. Should other readers (such as czeslaw) be interested in the material, well, they can follow up in whatever way they like.

If the material you have is not on the net, then why not provide a reference (book title, paper ref, etc)?

Are there some particular characteristics of the material that lead you to conclude it would be inappropriate to post here? =D> =D> Hear hear!

OK, so you know about the 'particle-wave' dual nature of electrons (and photons, and neutrons, and ...), don't you? This means that you have a 'wave' nature as well as your obvious 'particle' nature, right? Now, in what way might your 'wave' nature have some relevance? Well, perhaps you could consider 'teleporting' yourself to the Moon (OK, this is quantum tunneling, not the same thing, but not totally different either)? It's 'theoretically possible', right? So why hasn't some entrepreneur started a business in Moon tourism, using quantum tunneling as a means of transportation?It's good that you're asking a question. However, ATM isn't really the place for this.

However, here are some things you might like to consider:
- what is the magnitude of a charge imbalance in a body which completely stops incoming CRs, resulting from the charge imbalance of those CRs?
- a body absorbing CRs is, of course, not totally isolated in space; expressed as a % of the local (plasma) particle density, what is the 'space density' of CRs?
- the term 'cosmic rays' is used for particles whose energy exceeds a certain (minimum) threshhold, right? What about 'incoming' particles that have energies below this threshhold? What is their number/energy density? particle composition? etc?
- assume CRs don't collide with (IPM, ISM) plasma particles; assume all CRs above a threshhold are +ve; the CRs are then a 'current', right? In which direction is the current flowing? How does the plasma through which the CRs are passing respond (to the fast moving electric fields of the protons etc)?

We have usualy a technological problems to use a teorethical possibilities, We know abot quantic computers but it is difficult to make it now, but in the future... ?

A Cosmic Rays are very rare - about 2 500/sm^2 particles in the upper Earth's atmosphere. The current created by CRs is very tiny. But, if such protons + hit an object, it will be charged till its capacity. That way a space filled with + protons might be + charged.
Where are the electrons then. Are they captured by a magnetic field of AGN, supernovae, magnetars, clouds of plasma ?

Hi Tusenfem. I wish you happy holidays but if you only would have a computer by hand jump into ATM. Your critique is welcome.

I have always posted publicly where possible. And indeed, the material is inappropriate to post here.

I have a couple of books I would like to offer to lend you, but I am quite possessive about them, and don't want to make the offer to everyone. More details via email.

Sorry everyone.

Regards,
Ian Tresman

Thanks Ian.

Might it be possible to give the references (title, author, date, publisher), for us all?

• Cosmical Electrodynamics, 2nd ed. (1963), Hannes Alfvén & Carl-Gunne Fälthammar
  
• Cosmic Plasma (1981), Hannes Alfven

Regards,
Ian Tresman

I've obtained copies of both books, are there certain sections you would recomend?

I guess it depends where you're at with regards to space plasmas, and in particular, Alfvén's persepective on electricity in plasmas. In Cosmic Plasma (1981), I would suggest that the first 3 chapters are good reading as they offer a good case for the general underestimation of electric currents in space plasmas. The rest is quite an interesting read anyway, though I'm not convinced by his sections on "anti-plasma" (or ambiplasma).

Cosmical Electrodynamics is somewhat more technical, but Chapter 5 is worth the read.

With regard to applications to the interstellar medium (ISM), Cosmical Electrodynamics has a section 4.2.2 Similarity Transformations, which gives an indication of how the very tenuous ISM might be expected to behave.

Regards,
Ian Tresman