‘Sonic Booms’ in Space Linked to Star Formation

Article written: 14 Apr , 2011
Updated: 24 Dec , 2015


Its true there is no sound in empty interstellar space, but the Herschel space observatory has observed the cosmic equivalent of sonic booms. Networks of tangled and tremendously large gaseous filaments seen within clouds of gas and dust between stars are likely to be remnants of slow shockwaves from supernovae, Herschel scientists say. And surprisingly, no matter what the length or density of these filaments are, the width is always roughly the same, about 0.3 light years across, or about 20,000 times the distance of Earth from the Sun. This consistency of the widths demands an explanation, scientists say.

And it’s possible these shockwaves could generate sound within an interstellar cloud – if something were there to hear it.

“Although the density in an interstellar cloud is lower than in a very good vacuum on Earth there are molecules in the order of 10^8 per cm^3” said Goeran Pilbratt, ESA’s Herschel mission scientist. “That should be enough for sound to propagate, apart from the fact that we do not have the instruments to measure it.”

Filaments like this have been sighted before by other infrared satellites, but they have never been seen clearly enough to have their widths measured. Herschel is seeing that the width of these filaments is nearly uniform across three nearby clouds: IC5146, Aquila, and Polaris. The Herschel team, lead by Doris Arzoumanian, Laboratoire AIM Paris-Saclay, CEA/IRFU, made observations of 90 filaments, and found all had nearly identical widths. “This is a very big surprise,” Arzoumanian said.

The network of interstellar filaments in Polaris as seen by Herschel. Credits: ESA/Herschel/SPIRE/Ph. André (CEA Saclay) for the Gould Belt survey Key Programme Consortium and A. Abergel (IAS Orsay) for the Evolution of Interstellar Dust Key Programme Consortium.

Also, newborn stars are often found in the densest parts of these filaments. One filament imaged by Herschel in the Aquila region contains a cluster of about 100 infant stars.

The Herschel team said their observations provide strong evidence for a connection between interstellar turbulence, the filaments and star formation.

“The connection between these filaments and star formation used to be unclear, but now thanks to Herschel, we can actually see stars forming like beads on strings in some of these filaments,” said Pilbratt.

Comparing the observations with computer models, the astronomers suggest that filaments are probably formed when slow shockwaves dissipate in the interstellar clouds. These shockwaves are mildly supersonic and are a result of the huge amounts of turbulent energy injected into interstellar space by exploding stars.

They travel through the dilute sea of gas found in the galaxy, compressing and sweeping it up into dense filaments as they go. As these “sonic booms” travel through the clouds, they lose energy and, where they finally dissipate, they leave these filaments of compressed material.

Interstellar clouds are usually extremely cold, about 10 degrees Kelvin above absolute zero, and this makes the speed of sound in them relatively slow at just 0.2 km/s, as opposed to 0.34 km/s in Earth’s atmosphere at sea-level.

Sound travels in waves like light or heat does, but unlike them, sound travels by making molecules vibrate. So, in order for sound to travel, there has to be something with molecules for it to travel through. On Earth, sound travels to your ears by vibrating air molecules. In deep space, the large empty areas between stars and planets, there are no molecules to vibrate.

Read the team’s paper: Characterizing Interstellar Filaments with Herschel in IC5146

Sources: ESA email exchange with Pilbratt

41 Responses

  1. iantresman says

    “It’s true there is no sound in empty interstellar space”

    Isn’t it that the the interstellar plasma does carry sound waves, it’s just that their intensity is too low to measure. Apparently a branch of magnetohydrodynamics called kinetic-MHD describes the sound velocity in a collisionless plasma. See:

    Reinaldo S. de Lima et al, “Evolution of Magnetic Fields in the IGM: Kinetic MHD Turbulence” in Cosmic magnetic fields: from planets, to stars and galaxies, proceedings of the 259th Symposium of the International Astronomical Union, held in Puerto Santiago, Tenerife, Spain, November 3-7, 2008, ISBN 0521889901.

    • Olaf says

      Isn’t it that the the interstellar plasma does carry sound waves,
      Nope. The particles are too far to carry sound.
      This is just particles catching up on other particles as density waves and some of them collide thus slowing down creating a denser area..

      There is no magical EU to be found here. Your quote is the only reference to “plasma”

      • Hon. Salacious B. Crumb says

        Olaf. You are perfectly correct about the density waves, but it is also influenced by what is happening in the surrounding medium.
        Massive stars blow into supernova, the nebulosity being a mix of gas that has not dropped in a stellar furnace (mostly neutral hydrogen and some H-II), mass loss for the active or long dead stars, and various ejected emissions caused by stellar evolution processes, etc. It is the historical combinations of this “little mess” that is likely creating the complex structure in this region of space. Magnetic fields do exist, but the field strength is quite piffling compare to the other forces at work here. No doubt there is significant magnetic field fragmentation which is disorganised and is facing in all sorts of directions. (It is like the magnetic rocks of the Earth, where all the little magnets are in almost random directions, even though the entire Earth’s field has obvious magnetic field symmetries.)

        An arXiv paper release yesterday; Berkhuijsen, E.M., Flecther, A., “Density PDFs of Diffuse Gas in the Milky Way“; http://arxiv.org/abs/1104.2410

        “The… authors found that for a large enough volume, and for a long enough simulation run, the physical processes causing the density variations in the ISM [InterStellar Medium] in a galactic disc can be regarded as random and independent events. The medium is inhomogeneous on a local scale, but in a quasi-steady state on a global scale.”

        Exactly the same applies to all the mag. fields as well.

        Thanks too, for your other excellent points made here.

  2. Jon Hanford says

    It’s interesting to compare the Herschel view of IC 5146 (and the adjoining “dark” nebula B168) with a view in visible light: http://www.dutchdeepsky.com/ic5146_lrgb_101009_hr.jpg

    Of course at the wavelengths used for the Herschel image, this dark absorption nebula appears quite bright. B168 is not too difficult to spot visually with good binoculars or a telescope with a suitable field of view (and a suitably dark, transparent sky of course). The sheer number of stars in this region of the sky certainly helps boost B168’s visibility as well.

    Coordinates for IC 5146 are RA 21h 53.5m, dec+47° 16?

    Source – Wikipedia: http://en.wikipedia.org/wiki/IC_5146

  3. iantresman says

    I don’t understand why the distance apart of the interstellar particles makes a difference in a collisionless plasma?

    I also don’t understand why you bring up EU, I made no reference to it, and it clearly has no relevance here. I don’t even think there is a PU view on it.

    Another source suggests that the sound velocity in the interstellar medium is about 1km/s. See:
    James Lequeux et al, “Multi-fluid shocks in a weakly ionized gas“in The interstellar medium, Volume 941, Issue 7834 of Astronomy and astrophysics library.

    That’s two sources that suggest that the interstellar medium carries sound wave, and I have acknowledged that it would hardly be detectable. So where have the two sources gone wrong?

    • Olaf says

      I don’t understand why the distance apart of the interstellar particles makes a difference in a collisionless plasma?
      Where exactly does that first article claim that it creates sound? Unless you quote mined that article and took the only sentence that had the word “sound” in it. And as far as I know the world “sound” has multiple meanings. For example Solid.

      • iantresman says

        >as I know the world “sound” has multiple meanings.

        That would make sense. The Universe Today article suggests “there is no sound in empty interstellar space”, so indeed, there must be a slightly different meanings.

    • Olaf says

      Ok I read the articles.

      Now explain us in your own words what the word “sound” means in both articles you quoted. I doubt that you actually understand what they really say.

      • iantresman says

        That’s what I was hoping someone else might be able to do.

      • Hon. Salacious B. Crumb says

        I also did read these articles.

        As or the word “sound”, a useful definition is; “Vibrations that travel through the air or another medium and can be heard when they reach a person’s or animal’s ear.”

        I suppose in a nebulae or the interstellar medium in the Milky Way, the process might be better described as “soundlessness.” (Sound without actual sound?”

        Your point here is quite valid. Definition is important, which seem of little interest to those whose astronomical organisations release press notification and make things just on the principle of “dumber for dummies.”

  4. Carl Sagan's Roach Clip says

    I knew before I even reached the comments that iantresman would have some article to link about plasma.

    If iantresman links an article in space – does it make a sound?

  5. Hon. Salacious B. Crumb says

    Interesting story. I think there is a big difference to sound wave and density waves. One could argue, that it is the motion of the gas being influenced by relatively fixed surrounding gravitational sources and that these transfer variations in the density as the gas.
    It is also interesting that the article only mentions supernova detonations and their expanding shells being the possible cause. There are other possible explanations. I.e. Expanding H-II regions, galaxy density waves, stars exhaling their atmosphere into interstellar space, and even and planetary nebulae. I think the picture of galaxies fool everyone to think they are nice order environments, but near the places of the density waves, they are clearly more chaotic (as Herschel shows here.)
    Sound waves and sonic boom are a bit to simplistic, which I assume is basically the dumbing-down by some publicity officer voicing general information to the world. Neither are relevant as nothing is aural. It is just like saying ocean waves are exactly like sound waves. Well it is true they have similar properties, but you don’t hear ordinary ocean waves, unless they are lapping against the boat or under a white-horse throwing foamed during a howling gale. The image here too, almost looks like rolling sea on the ocean.
    Needless to say, the sound generated here is merely a faint delicate whisper or zephyr (love this word!) on the interstellar breeze.
    As for any magnetic field here, it is clear they are not very organised, and are mostly more chaotic compared to the moving by the turbulence in the nebulosity. It is likely, when star are “seeding” (for want of a better word, or condensing does the magnetic field come organised as the nebulosity accretes towards shining stardom. Whatever the field strength of the 0.1 parsecs (the origin of the 0.3 light-years value from the actual calculations) filaments no doubt the energy of the shockwave and the interstellar medium it runs into are the fore-bearers of the foetal star that are yet to emerge.
    Thanks for the interesting article. Good to see this Herschel mission is still producing magnificent results!

    • Hon. Salacious B. Crumb says

      Oops. “…filaments; there is no doubt much of the shockwave energy and the interstellar medium it runs into, are the fore-bearers of the foetal stars that are yet to emerge from their nurseries.”

      Gosh, I’d kill sometimes for a basic editor!

      C’est pas, de la tarte? (Comme négatif habituellement implicite par le Français.) Umm. Au moins je pense ainsi

    • Torbjorn Larsson OM says

      Yes, it is difficult to know if it is sound waves as such, but as I read the paper the final effective energy dissipation quite naturally seems to be hit at when the system gets down to sound speed (which is what set the scale for, and preserves, the structures). What amount of large scale density variation can be interpreted as sound phenomena and what is still identifiable as shock at that time is probably a question for modeling.

      Incidentally, the ambiguity should go both ways. What we can hear as ‘sound’ are pressure variations that can in cases come from other sources than sound waves, shock waves is a good example. Though I assume if you hear one, it may be the last you hear…

      • Hon. Salacious B. Crumb says

        Yes, you have a point. Though we should be analogous as to interpret the “loudness” of the sound to the “brightness” or “light extinction” in the dark portions (of the imaged intergalactic medium) as the crest and dips of the uneven density across the field?
        It is really the density of material we observe in the telescope and not the nature of the acoustics of the material. Sound is useful as an analogy from radio telescopes, but in the infrared portion is seems just a little odd. If we considered, say ultraviolet or X-ray, does it make sense to talk as the medium in which it travels as “sound.”

        (Another analogy is those fish or eels with electric sensors all over their bodies. Do they sense there prey by the “sound” generated in the water or by “touch.”)

        It is unlikely anyone will ever hear the Interstellar Medium (…but it would be a excellent name for a modern pop group!)

      • Torbjorn Larsson OM says

        Absolutely, excellent analogies.

  6. Hon. Salacious B. Crumb says

    Quant à la cosmologie de plasma ou à l’univers de plasma, les champs magnétiques dans le milieu interstellaire peuvent jouer une petite partie, mais elle mineur comparé aux effets de l’attraction universelle par le gaz ou les nuages de poussière énormes.

    Comme d’habitude, notre ami ici a l’audition sélective, methinks. Le seul bruit que nous devrions être audition de lui est silence complet. Ne pensez-vous pas ?

    • iantresman says

      I don’t think you have to be able to hear a sound, in the range heard by humans, for something to be defined as a sound. I think the mechanism is the defining factor. After all, dogs hear much higher sounds that we can, and whales much lower sounds. All though we can’t hear them, they are still sound waves.

      The affect of magnetic fields and gravity on ions and neutrals in the interstellar medium can be calculated. Depending on the magnetic field strength, and mass of a cloud, I am sure there are regions where each is significant.

    • Hon. Salacious B. Crumb says

      N’est pas ce vraiment ce que j’ai dit du tout. (Tellement voici la traduction brute.)

      As for plasma cosmology or with the plasma universe, the magnetic fields in the interstellar environment can play a small part, but it [is] minor compared with the effects of the gravitation by gas or the enormous clouds of dust.

      As usual, our friend here has selective hearing, methinks. The only noise that should be hearing of him to us is complete silence. Don’t you think?

      • postman1 says

        HSBC- Love you commentary, as usual. Too bad my french is so darn rusty. Back in the early 70’s I was entirely fluent, c’est la vie.
        I read most everything on this site, purely for the educational value, and sometimes the comments are the most informative part of all. Thanks, guys and gals.

  7. Member
    DrNothing says

    Hate being picky, but there’s far too many errors in this one small sentence fragment to not cry about, “10 degrees Kelvin above absolute zero”… Kelvin is not a type of ‘degree’, and 10 Kelvin by definition more than implies the ’10’ is above absolute 0 as that would be 0 Kelvin. Awkward and multiple times redundant. Other than that, fascinating story. I like filaments and this size issue is odd. One would think that if there were a process derived from the shock waves’ terminations that would exert an amount of force that had a constant or some such determining the termination strength of it’s dissipating energy, that the density of the medium within which it’s propagation ceased would be a variable effecting the amount of affected combining, thus the thickness.

    • Torbjorn Larsson OM says

      Maybe I’m misunderstanding. If you ask what effect density would have on the filament size, it is an excellent question.

      If sound speed is involved as implied, to first order sound speed is independent of density (and pressure) in ideal gases.

      • Member
        IVAN3MAN_AT_LARGE says

        Torbjörn, your link — iznogoud. You forgot to include the URL.

      • Torbjorn Larsson OM says

        Ah, thanks! Sound speed in ideal gases.

        At least we got some comic out of it. [Iznogoud the Infamous – still not caliph.]

      • iantresman says

        I agree that the sound velocity is independent of the plasma density, but will be different for the different ion species. It also seems that in plasmas, a sound wave is often referred to as an “ion acoustic wave“. Perhaps that avoids confusion with a “sound” that we can’t actually hear.

      • Torbjorn Larsson OM says

        Irrelevant in the model. These clouds were diffuse gas and dust clouds and it was precisely the prediction from turbulence and not magnetic fields or gravity that was successfully tested with the observations. “While magnetic fields may play an important role in channeling mass accumulation onto the densest filaments (e.g. Goldsmith et al. 2008; Nakamura & Li 2008), our Herschel findings appear to be consistent with the turbulent picture.”

        So little relevance for plasma effects here, if even the clouds were ionized in the first place. Plasma is _not_ “99.999 %” of interstellar clouds. Maybe more like 00.001 % of large scale mass accumulation effects if the paper is right!? 😀

  8. Olaf says

    First let’s put stuff into perspective.

    Interstellar space does not equal Plasma. It could be plasma but does not need to be in a plasma state.

    Second plasma state does, equal having electric fields and and magnetic fields. It could have magnetic fields but does not need to have it.

    Calling everything plasma is a deliberate attempt to deceive and mislead by hiding away the real properties. Calling interstellar clouds plasma, is completely wrong because you hide the fact that these clouds could also be in a none-plasmatic state. Or when it is in a plasma state that it has an average neutral charge and thus no electrical field and magnetic field.

    The sun is such an example, it is in a plasma state (on the surface) but the complete charge is neutral since it contains equal positive and negative charge. Local turbulence on the sun can create local magnetic lines only.

    If you are an electrical engineer, you might actually compare plasma to what you know in TL lights, but in space this plasma behaves completely different than in the TL lights. In space the positive charges also move, in TL lights positive charges cannot move into the wires. Only negative charge called electrons can move through the wires and through the plasma. Space behaviour of plasma and plasma in your electrical equipment behaves differently.

    • Olaf says

      Also in space to have a gas shaken into a plasma state, you need to have an energy source that bumps off the electrons from the atoms and keep doing this all the time. Because if this energy source stops then the negative charges will attract the positive charges and in a certain time period they will find each other and become gas in a none-plasmatic state.

      A nearby star could shake the gas into a plasma state, also radiation could do that.
      But far away from any stars, gas will revert to a none-plasmatic state over time.

      • iantresman says

        I think it may be the other way around, Intergalactic space which is even further away from stellar sources than interstellar space, is considered to be a fully ionized plasma.

        Ions will only lose energy if it has somewhere to go. By volume, 99.999% of the universe is a plasma (largely intergalactic space, and much of interstellar space), so where is the plasma going to lose energy to?

      • Hon. Salacious B. Crumb says

        Asolutely wrong, wrong, wrong… Same old record playing the same old tune!

        In fact, it is precisely the opposite, and even the magnetic fields are incoherent and not formed. Hence; Where is the observation evidence for this or its is “fully ionized plasma”? it is a unsupported assumption by you made without any real support by astrophysicists.
        Think about it. How did the alleged plasma become ionised? It had to be near an energy source like stars or galaxies. You cannot prove that the majority of the matter within intergalactic space is neutral or ionised. (No known magnetic fields exists there, and there is no observation to prove it!)

      • iantresman says

        It is not clear what you are claiming is absolutely wrong, unless I assume that you are referring to everything I wrote.

        It is interesting that you say in one sentence “Where is the observation evidence for this or its is “fully ionized plasma”, and in another you know that “it is precisely the opposite, and even the magnetic fields are incoherent and not formed”.

        Let’s try and move away from this idea of proof. You should know that there is no such thing. The number of sources stating that the intergalactic medium is considered fully ionized, is considerable, eg. (http://) goo.gl/wdJBT

        And here’s a recent paper which provides evidence of intergalactic magnetic fields:

        Shin’ichiro Ando, Alexander Kusenko , “Evidence for Gamma-Ray Halos Around Active Galactic Nuclei and the First Measurement of Intergalactic Magnetic Fields”, Astrophys. J. 722, L39 (2010) (Arxiv).

      • Hon. Salacious B. Crumb says

        Yes, exactly. “…unless I assume that you are referring to everything I wrote.'”
        Both these sentences are wrong, and exactly for the reasons as stated.

        There is absolutely no proof of universal intergalactic magnetic fields. are everywhere. Those that are stating to be observed are between interacting galaxies or surrounding galaxies.
        The only evidence of intergalactic fields are from the behaviour of light between the source and the observer. Many are particularly from X-ray emissions. Cherry picking one or two examples is quite far from saying this is a universal phenomena.
        I.e. I know the universe is expanding be redshift observations of millions of galaxy spectra. I don’t know the intergalactic magnetic fields exist, because there are few observations to support nor is their evidence that it applies in all directions. Hence You cannot say; ” interstellar space, is considered to be a fully ionized plasma.”, as there are few observations to support it, and there is little evidence universal intergalactic fields. — either coherent or incoherent. Plasma to some extent may exist between the galaxies, but as we cannot directly observe the general magnetic intergalactic fields. This is mostly as from the tiny density of about 10^-31 grams per cubic centimetre. (the magnetic field generated by the earth’s core by comparison averages about 3000 grams per cubic centimetre — a mere difference of about 10^34 orders of magnitude.) So the plasma simply cannot hold coherence of the field as there is really nowhere for the electrons to flow. That is why much of the hydrogen between galaxies is not really a plasma, as it cannot have or sustain a flow of electrons to make the hydrogen behave as plasma.
        Such really simple physics should be easy enough for even you to understand!

      • DrFlimmer says

        Ions will only lose energy if it has somewhere to go.

        Yes, radiation can go anywhere. So, the plasma will lose energy by radiation. And why? Because it has a temperature. And the radiative flux of anything with a temperature goes like ~T^4.
        As long as there is no energy source, everything, even a plasma, will cool and, therefore, lose energy.

        It is true that there is plasma in the intergalactic space IN clusters of galaxies. In fact, this medium is quite hot, since it glows brightly in X-rays (so the temperature must be quite high as one can calculate with the help of Wien’s displacement law). The energy sources, in this case, are galactic collisions or the feedback of active nuclei (AGN).

        There can also be magnetic fields in the intergalactic space. However, as iantresman’s arxiv-link says: “B_{IGMF} ~ 10^{-15} G”. That’s not really much (enough for the stated effect, but not to “do” anything).

        How the picture looks like in truly empty space, like in the large voids, is something else. It is likely, from my perspective, that there is really nothing.

  9. iantresman says

    Olaf wrote: “Interstellar space does not equal Plasma”

    Olaf wrote: plasma [..]could have magnetic fields but does not need to have it.
    Agreed. But as far as I know, all space plasmas are magnetic.

    Olaf wrote: “plasma state that it has an average neutral charge and thus no electrical field and magnetic field.”
    Plasma is quasi-neutral. This does not mean that it has no electrical field and magnetic field. It does mean that overall, it tends towards neutrality.

    Olaf wrote: “Calling interstellar clouds plasma, is completely wrong”
    Not necessarily. Neutral clouds with even a small degree of ionization may behave like a plasma. For example:

    “The greater proportion by far of interstellar medium, however, exists in the form of neutral hydrogen clouds referred to as H I regions. Because the heavy atoms in such clouds are ionized by ultraviolet radiation, they are also considered to be plasma, although the degree of ionization is probably only one part in 10,000” — “The Britannica Guide to Matter” (page 219). Other references available, eg., Alfvén and Falhammar in Cosmical Electrodynamics

    Calling neutral regions “gases” when they may behave like plasmas, could also be misleading.

    • Hon. Salacious B. Crumb says

      So many wrong and specious ideas here it is hard to know where to start;

      Wrong. “But as far as I know, all space plasmas are magnetic.”
      We don’t Even if there is plasma in intergalactic space, the field is incoherent. Worst there is little evidence to support plasma dominates that intergalactic space.

      “It does mean that overall, it tends towards neutrality.”
      Simplest one to prove this wrong. Then it isn’t plasma.
      (stop using a broader brush with the term plasma. For it to be plasma it has to be HIGHLY INONISED not ionised like in chemical reactions nor one or two electrons missing. (I.e. It is highly debatable if a hydrogen ion, as a simple proton is really defined as a plasma. How it is observed, what species it is, and the plasma composition (plasma chemistry), is still continuous subject. (even by plasma researchers!!!)
      For hydrogen it is the energetic electron that ionised the gas. In intergalactic space, you have to have a magnetic field to make it behave as a plasma. As we have shown, the magnetic field in incoherent, hence most of the hydrogen is NOT a plasma.
      (Very careful replying to this one, as I know a paper by a plasma physicist on plasma chemistry which would kill most of this nonsense!)

      Olaf is perfectly correct in saying “Calling interstellar clouds plasma, is completely wrong”. Your reply “Not necessarily. Neutral clouds with even a small degree of ionization may behave like a plasma. For example:” Really. “Small degree ionization” DOES NOT make it a plasma, then. (Sorry. Another deliberate half-truth.) Intergalactic plasma, that has not been proven to exist nor observed, made worst by the magnetic fields being actually incoherent.) Worst is you even contradict yourself, when you said “…interstellar space, is considered to be a fully ionized plasma.”
      It cannot be both, can it.

      As for “Calling neutral regions “gases” when they may behave like plasmas, could also be misleading.” What? Your immediate assumption here is if there is a magnetic field, then there must be a plasma. Yet, if we haven’t observed a weak or unobserved magnetic field, you cannot deduce that it is plasma. Really. Without evidence you cannot say this!

      (I notice you try and protect yourself by saying “may” and “could”, when the fact is you don’t actually know. It is good to be you realise the problems of absolutes, but you also have to be cautious not to be caught out by deliberate bias. To argue in this case, it is better to argue from known to unknown. I.e. Although it seems likely from the available evidence is like neutral regions “gases” are mostly ionised , the behaviour of these regions could also mimic those of plasmas. By X, Y or Z.” [That is a scientific argument. (If you ao have a BSc. as you claim, this sort of answer should be just second nature. As it is not your usual approach, I (we) can only concluded you are biassed or are being deliberately deceitful. Either way, you quickly lose the argument.)]

      Seriously, I think you have become so wrapped up in your own plasma propaganda, that you have clearly forgotten what a plasma and ionised gas is. You are caught up in the rhetoric you have forgotten even the most basic of astrophysical observation, theory, and evolution of evidence to explain the phenomena.

      Please be more careful when discussing the acceptable science. Most of what you say in this reply is not supported by either astrophysical or plasma physics community. It is bordering on “personal theory”, and has been already properly debunked by many commenters in many other Universe Today stories. It is disingenuous to pretend otherwise.

  10. iantresman says

    I wrote: “It does mean that overall, it tends towards neutrality.”
    HSBC wrote: Simplest one to prove this wrong. Then it isn’t plasma.
    (stop using a broader brush with the term plasma. For it to be plasma it has to be HIGHLY INONISED not ionised like in chemical reactions nor one or two electrons missing.”

    No, that is incorrect. A plasma may be neutral overall, ie. equal numbers of positive ions and negative electrons, but it is still a plasma because it contains a significant number of ions. By significant, I do not mean a large number, but sufficient numbers for it to influence and dominate any neutrals.

    For example, “Note that the ionization degree of the ionosphere is very low at low altitudes, but nevertheless the gas behaves like a collisional plasma” — Physics of Space Storms: From the Surface of the Sun to the Earth
    By Hannu Koskinen (page 50)

    The properties of a weakly ionized plasma are obviously different from a fully ionized plasma, but as numerous sources attest, a partially ionized gas, where the degree of ionization is less that 1%, may behave as a plasma. That is not an opinion.

    Even more Sources

    “Note that plasma-like behaviour ensues after a remarkably small fraction of the gas has undergone ionization. Thus, fractionally ionized gases exhibit most of the exotic phenomena characteristic of fully ionized gases.” — ichard Fitzpatrick, Introduction to Plasma Physics: A graduate level course,F “Introduction: 1.2 What is plasma?” page .6. (http://) goo.gl/0key8

    “A partially ionized plasma has a degree of ionization that is less than 1. Examples include the ionosphere (2×10^-3)” — Francis Delobeau, The Environment of the Earth, (1971) page 13. (http://) goo.gl/dcbtH

    ““The greater proportion by far of interstellar medium, however, exists in the form of neutral hydrogen clouds referred to as H I regions. Because the heavy atoms in such clouds are ionized by ultraviolet radiation, they are also considered to be plasma, although the degree of ionization is probably only one part in 10,000? — “The Britannica Guide to Matter” (page 219)” (http://) goo.gl/r501s

    All these sources state that a gas with a low degree of ionization, less than 1%, and in some cases less than 1/100%, may be classified (and hence behave) as a weakly ionzed plasma.

    • Hon. Salacious B. Crumb says

      Everything you have stated here is not applicable to intergalactic medium!!!!!!!!</B

      The ionosphere, aurorae, interstellar medium, etc, are relatively dense compared to the intergalactic space. As usual you just avoid talking about intergalactic space and then just talk about everything else!

      If you cannot stick to the actual debated subject, then there is no point to discuss this any further.

      • Hon. Salacious B. Crumb says

        Oops. Apologies for the inadvertent shouting. Again…

        Everything you have stated here is not applicable to intergalactic medium!!!!!!!!

        The ionosphere, aurorae, interstellar medium, etc, are relatively dense compared to the intergalactic space. As usual you just avoid talking about intergalactic space and then just talk about everything else!

        If you cannot stick to the actual debated subject, then there is no point to discuss this any further.

  11. iantresman says

    I was discussing and provided citations for what defines weakly ionized gases as plasmas. I had previously provided references to the intergalactic plasma.

Comments are closed.