Wednesday, February 11, 2009

Mainstream Scientists Discover Magnetism



"And that the shooting stars are as it were sparks which glance off from the movement of the pole. And that winds are produced by the rarefaction of the air by the sun and by their drying up as they get towards the pole and are born away from it. And that thunderstorms are produced by heat falling upon the clouds. And that earthquakes come from the upper air falling upon that under the earth; for when this last is moved, the earth upheld by it is shaken." -- Hippolytus, Refutation of All Heresies, "About Anaxagoras"

Eureka! But still they are afraid to call it a Birkeland current. And they are forgetting Winston Bostick and Anthony Peratt. Science in amnesia: First laboratory experiment to accurately model stellar jets explains mysterious 'knots'. (Hat tip: Anaconda)

Some of the most breathtaking objects in the cosmos are the jets of matter streaming out of stars, but astrophysicists have long been at a loss to explain how these jets achieve their varied shapes. Now, laboratory research detailed in the current issue of Astrophysical Review Letters shows how magnetic forces shape these stellar jets.

"The predominant theory says that jets are essentially fire hoses that shoot out matter in a steady stream, and the stream breaks up as it collides with gas and dust in space—but that doesn't appear to be so after all," says Adam Frank, professor of astrophysics at the University of Rochester, and co-author of the paper. "These experiments are part of an unusal international collaboration of plasma physicists, astronomers and computational scientists. It's a whole new way of doing astrophysics. The experiments strongly suggest that the jets are fired out more like bullets or buckshot. They don't break into pieces—they are formed in pieces."

Frank says the experiment, conducted by Professor Sergey Lebedev's team in the Department of Physics at Imperial College London (www.imperial.ac.uk), may be the best astrophysical experiment that's ever been done. Replicating the physics of a star in a laboratory is exceptionally difficult, he says, but the Imperial experiment matches the known physics of stellar jets surprisingly well. "Lebedev's group at Imperial has absolutely pioneered the use of these experiments for studying astrophysical phenomena. The collaboration between Imperial and Rochester has been going on for almost 5 years and now it is bearing some extraordinary fruit."

At Imperial, Lebedev sent a high-powered pulse of energy into an aluminum disk. In less than a few billions of a second, the aluminum began to evaporate, creating a cloud of plasma very similar to the plasma cloud surrounding a young star. Where the energy flowed into the center of the disk, the aluminum eroded completely, creating a hole through which a magnetic field from beneath the disk could penetrate."

The field initially pushes aside the plasma, forming a bubble within it, says Frank, who carried out the astrophysical analysis of the experiment. As the field penetrates further and the bubble grows, however, the magnetic fields begin to warp and twist, creating a knot in the jet. Almost immediately, a new magnetic bubble forms inside the base of the first as the first is propelled away, and the process repeats.

Frank likens the magnetic fields' affect on the jet to a rubber band tightly wrapped around a tube of toothpaste—the field holds the jet together, but it also pinches the jet into bulges as it does.

"We can see these beautiful jets in space, but we have no way to see what the magnetic fields look like," says Frank. "I can't go out and stick probes in a star, but here we can get some idea—and it looks like the field is a weird, tangled mess."

Frank says other aspects of the experiment, such as the way in which the jets radiatively cool the plasma in the same way jets radiatively cool their parent stars, make the series of experiments an important tool for studying stellar jets. With this new model, he says, astrophysicists do not have to assume that the knotted jets they see in nature mean some unknown phenomenon interrupted the jets' flow of material.

Now, says Frank, some experiments that were once far beyond astrophysicists' reach have been, literally, brought down to Earth.

12 comments:

  1. YES, UNIVERSE TODAY DID FORGET BIRKELAND CURRENTS

    And I admit that in my comment I left that out. I didn't forget, but decided to engage a little, "don't stampede the elephants" tactics. I wanted to stick as close to the Post and linked scientific article as possible. I thought this approach would be the most effective way to persuade open-minded readers that these plasma jets are a function of electromagnetic forces.

    While it's a known and recognized physical law that electric currents cause magnetic fields, most casual followers of "modern" astronomy have never heard that physical law.

    This is due to modern astronomy's fixation on "black holes", and other objects, "neutron" stars, that are a product of "modern" astronomy's desire to support and protect the gravitational model.

    But individual casual followers of "modern" astronomy can't be held responsible for that situation.

    The "leading lights" and mainstream science media are responsible for this sad state of affairs.

    The best that can be done is to introduce the casual followers to the concept that electric currents cause all the magnetic fields that are observed and measured in the Universe.

    This is an 'easy sell' because it's the facts and the logic is crystal clear.

    Gradually, more people will understand this concept and once "electric currents cause magnetic fields" takes hold then the rest of Plasma Cosmology will get an increasingly firmer grip.

    Then the belief in "big bang, black hole" theology will crumble.

    So provide people the basic facts and their innate curiousity will lead them in the right direction.

    The average person wants to understand what is actually happening in their world and the larger sphere beyond that.

    It's only the professional astronomers and their minions that have self-interest who ignore the scientific evidence.

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  2. WANT "BIG", TRY GALAXY FILAMENTS ON FOR SIZE

    Yes, these are the grand daddies of them all, galaxy filaments, also known among supporters of Plasma Cosmology as galactic Birkeland currents.

    Galaxy filaments, galactic Birkeland currents in all their finest glory.

    Also, here is the galactic walls, or sheets. Of course, it is also known that electric currents will form into sheets. And double layers will form into sheaths.

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  3. WHERE WHITE IS BLACK AND "dark" matter holds up the Universe...Not!

    When it comes to reality, "modern" astronomy is in the year 1984.

    The galaxy filaments have an uncanny resemblance to an electricity grid.

    The concept of electric current filaments jumps out at you.

    But not if you are a member in good standing in "modern" astronomy.

    Instead, you claim that "dark" matter acts as the Atlas of the Universe holding it together, never mind that "dark" matter has ever been detected.

    And when you present an image, black becomes white, a white galaxy filament image that is.

    It's a nice negative image to present. I like the contrast between the two images.

    But since there has never been any observed "dark" matter, what do you have at brass tacks:

    An unproven hypothesis ("dark" matter) holding up a dubious theory ("gravity only model").

    That's called one shaky house of cards.

    But consider this additional analogy: What does gravity act like? A possible analogy is honey.

    Pour some honey out of the bottle and it flows, but turn it slightly up and the "filament" gets very long and thin, but then at some point snaps back and contracts, something like gravity would do -- gravity only attracts.

    So, if gravity is like honey and pulls toward the center of mass, how would gravity get strung out in long filaments? No, it would tend to clot up and not form stable filaments.

    Electricity on the other hand, has the exact opposite tendency -- it flows from one place to another in filaments and sheets.

    And electric currents cause magnetic fields which in turn collect and constrict more electric currents (adding electrons and ions) which adds stability and duration of the current flow.

    So looking at the linked images, both black and white, what looks more probable, gravity held up by the Atlas of "dark" matter, or electromagnetic currents flowing between galaxy clusters?

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  4. THE COMPUTER ANALOGY

    Since analogies have been touched on, another analogy is appropriate.

    Gravity only attracks.

    Electromagnetism attracks AND REPELS.

    That's like one computer that operates on the "0", "1" system (all computer systems) and one computer that operates on the "0" system.

    Well, obviously, the computer on the "0" system wouldn't work.

    The difference is night and day, or in this case, gravity and electromagnetism.

    Now, to be fair to the "gravity only model", the proponents state that gravity causes a "repulsion" of sorts by causing thermal expansion of matter. But is thermal expansion of matter capable of forming all the jets and particle beams observed in the Universe?

    No.

    And does thermal expansion cause the level of electric currents necessary for the magnetic fields observed.

    Not likely.

    Thermal expansion simply doesn't provide the focussed energy observed in the Universe.

    Whereas electric currents in plasma environments are self-organizing.

    Filaments and sheets of electromagnetic currents are the ubiquitous outcome in a plasma environment such as we have in the Universe where over 99% of the matter is plasma.

    Here is the Electric Universe explanation for galaxy filaments: Galaxy Filaments, July 23, 2004(thunderbolts.info) -- "In an Electric Universe, the observed association of non-thermal radio filaments (NRF's) with star-forming regions is expected."

    Admittedly this POD concerns itself with galactic filaments toward the center of the Milky Way galaxy, rather than Extragalactic filaments as presented in the prior posts, but the concepts are the same.

    Now, since I've been using the images it seems appropriate to link the Wikipedia entry for Galaxy filament.

    Please review the Wikipedia entry.

    Then let me pose a question: Does all that "dark" matter acting as Atlas to hold together the Universe make sense?

    Or is "dark" matter only an artifice or sophism to hold together the gravitational model?

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  5. DOUBLE CHECKING THE THEORY

    This writer is making a powerful claim:

    "Filaments and sheets of electromagnetic currents are the ubiquitous outcome in a plasma environment such as we have in the Universe where over 99% of the matter is plasma."

    If the above quote is in fact reality. The Plasma Cosmology theory undoubtedly matches reality.

    So better double check it.

    In fact, that objection is one of the most common made by "gravity only model" proponents.

    "There isn't enough charge seperation to fuel the Electric Universe theory."

    But, very little scientific evidence has been presented to contradict the assertion that the Universe is over 99% plasma, by definition existing in a state of charge seperation.

    Here is a chart showing various elements in a state of ionization detected in a specific location in space:

    Mg XII -- Magnesium with all 12 of its electrons missing
    Ne X -- Neon with all 10 electrons missing
    Ne IX -- Neon with all but 1 electron missing
    O VIII -- Oxygen with all 8 of its electrons missing
    O VII -- Oxygen with all but 1 electron missing
    N VII -- Nitrogen with all 7 of its electrons missing
    C VI -- Carbon with all 6 of its electrons missing

    The chart is taken from this article: Charge Separation in Space, August 3, 2004(thunderbolts.info) -- "One of the basic assumptions of astrophysics today is that electrical forces play no part in cosmology because “you can’t get charge separation in space”. But x-ray images of space objects tell a different story."

    What is relevant to this argument, which will be subsequently apparent is that there is a number of elements with various levels of ionization (missing electrons).

    'Double layers' are the key to active charge seperation that leads to unbiquitous electric currents in the Universe.

    Definition from the Plasma Dictionary:

    "A double layer is an electric charge separation region that forms in a plasma. It consists of two oppositely charged parallel layers, resulting in a voltage drop and electric field across the layer, which accelerates the plasma's electrons and positive ions in opposite directions, producing an electric current. Large potential drops and layer separation may accelerate electrons to relativistic velocities (ie close to the speed of light), and produce synchrotron radiation. Double layers may be found anywhere that plasmas are found, from discharge tubes to space plasmas to the Birkeland currents supplying the Earth's aurora. And although plasmas are highly electrically conductive, a property that tends to neutralised charges, double layers may self-generate, or form when two plasma regions with different properties come into contact. The physics of double layers are also utilised to produce ion thrusters, such as the Helicon Double Layer Thruster. More at Wikipedia entry for double layer (plasma).

    "Double layers may be found anywhere that plasmas are found..."

    "And although plasmas are highly electrically conductive, a property that tends to neutralised charges..."

    ** "[D]ouble layers may self-generate, or form when two plasma regions with different properties come into contact."

    ** very important

    Why is the double stared passage so important?

    Because when you examine the Universe, "two plasma regions with different properties come into contact," occurs at a multiplicity of locations.

    Different properties turns out to be almost anything:

    Different element ions,
    The same element ions with different numbers of electrons removed,
    Different temperatures,
    and on it goes. The Wikipedia entry linked above (no friend to Plasma Cosmology) lists over ten different combinations of different plasma conditions in plasma regions that will cause a 'double layer' on contact with one another.

    The 'double layer' structure and process is the most important structure in the study of electromagnetism and, indeed, astrophysical electromagnetism because it is the engine of acceleration of both electrons and ions, as it were.

    In fact, 'double layers' are the engine of both acceleration and of charge seperation because a 'double layer' accelerates electrons and ions in opposite directions. (Promoting both electric current and charge seperation all in one stroke.)

    This is the base power platform for the electromagnetism system.

    And what is remarkable, as previously noted is that 'double layers' form essentially at the "drop of a hat" in terms of the plasma environment.

    So, in review, plasma is charge seperation by definition, but also charge seperation leads to self-organizing 'double layers', and thus electric current in a wide variety of plasma environments.

    Plasma Comology is basic physics and chemistry for the Universe.

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  6. Since the main article mentions Dr. Anthony Peratt and I know OIM has been banned from the Bad Astronomy blog, I thought I would repost my findings concerning a particular paper by Dr. Peratt for OIM's edification:

    The following are some excerpts from:

    ON THE EVOLUTION OF INTERACTING, MAGNETIZED, GALACTIC PLASMAS
    by Anthony L. Peratt and James C. Green
    Astrophysics and Space Science 91 (1983)

    and my reactions to them.

    “The geometry of the postulated galactic cloud model is cylindrical and contains, as the essential ingredient, and electric current whose flow is primarily in the axial direction but also having some degree of heliticity (Figure IV.8 of Alfven, 1981). Also present is a dipole magnetic field whose field lines are necessarily axial within the plasma”

    So Peratt is setting up a Birkeland current artificially by aligning the current flow with a magnetic dipole field by fiat. There is no reason given why this is expected to be a naturally occurring configuration. It is completely artificial, especially the cylindrical shape.

    “The galactic current is a result of an electromotive force (emf) induced by a rotating plasma in a magnetic field (Alfven, 1981). The energy of rotation thus represents the fundamental supply source. The current path is along the galactic axis of rotation, then fans out at distances greatly exceeding the extent of the denser plasma and returns back along the plane of rotation and also along the dipole field lines”

    O.K. So Peratt is essentially saying that the energy source that drives the whole thing is rotational kinetic energy of the plasma object rotating about its axis. Also note, the current comes back along the midplane of the object which in the case of quasars and active galaxies would mean perpendicular to the jets. Why is it we don’t see any returning jet in this direction?

    “In accordance with the basic model, an equal number of electrons and ions are arranged into a cylindrical column. The simulation is set up on SPLASH, a 3D, electromagnetic, and relativistic particle simulation code (Buneman et al., 1980). A 32 grid mesh defines the simulation spatial extent and, typically, the column extends 32 grids in length and has a diameter of 6 grids.”

    For two 35-kiloparsec diameter cylinders located 80 kiloparsecs apart (center-to-center) the extent of the grid is 115 kiloparsecs. Dividing it into 32 grid spaces means each grid element is 3,600 parsecs = 11,700 light-years wide. Note, that Peratt relies on someone else’s code. He didn’t write his own electromagnetic code to do the simulation.

    “With regard to computer economy, the time scale of the evolution is speeded up as fast as temporal resolution reasonably allows; the initial electron temperatures are in the 1-10 keV range and the mass ratio is mi/me = 16 (time scale compression, necessary for affordable simulation, can be achieved by decreasing the ion’s rest mass in relation the electron’s rest mass. The use of an artificial mass ratio will not significantly change the results of this study…”

    Oh boy! Peratt changes the rest mass of a proton from 1,840 times the electron rest mass to just 16 times the electron rest mass (reduced by a factor of 115). He does this in order to save computer time and then he claims it doesn’t affect the result of the simulation. For the electrons we have:

    T = (2/3)*K / k-Boltzmann

    where T is temperature in Kelvin, K is kinetic energy in eV, and k-Boltzmann is Boltzmann’s constant = 8.617E-5 eV per Kelvin. Thus a range of 1-10 keV is a temperature range of 7.7E6 to 7.7E7 Kelvin. The temperature of the plasma is in the millions of degrees. It will have HUGE radiative thermal losses that are not accounted for in Peratt’s model.

    (To Be Continued)

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  7. Continuation of Fisking of:

    ON THE EVOLUTION OF INTERACTING, MAGNETIZED, GALACTIC PLASMAS
    by Anthony L. Peratt and James C. Green
    Astrophysics and Space Science 91 (1983)

    “Fig. 1. Electric and magnetic radiation energies in arbitrary energy units. The unit vector z-hat defines the direction of the column azis.”

    We are presented with 3 charts showing electric radiation Ex, electric radiation Ey, and magnetic radiation Bz versus something called T which I took to mean time. The time axis goes from 0 to 1000 but I have no idea what the units are. They could be seconds, milliseconds, or millions of years. The y-axes go from 0 to 1 and they are in arbitrary units making them nearly useless in interpreting the results. All 3 curves have a sharp spike near the beginning and then a slower increase but with considerable statistical noise which is probably coming from instabilities in the numerical model. I have no idea why electric and magnetic radiation are separate since typically EM radiation has both the electric and magnetic fields together in space oriented at right angles to one another. So these charts are totally useless.

    “The electrons and ions, in response to the applied electric field, are accelerated in opposite directions and current starts to flow, and we record the conversion of the field associated potential energy into kinetic, magnetostatic, and radiation energies. Early in this stage of development the total radiated energy represents less than 1% of the magnetostatic energy which itself amounts to about 1% of the particle kinetic energies.”

    So the amount of radiation is miniscule at the beginning despite the charged particles being millions of degrees in temperature. Yeah, right. Apparently Peratt has never heard of the Stefan-Boltzmann law since he doesn’t mention it anywhere in his report.

    “In addition to deforming the plasmas, this produces a burst of synchrotron radiation (magnetobremsstrahlung) whose high-frequency electric field is polarized in the x-y plane, as shown in Figure 1. The radiation is thus directed along a narrow beam in the direction of instantaneous electron motion and linearly polarized at right angles to the magnetic field lines…
    For Cygnus A, the ‘prototype’ radio galaxy, we assume a mass M = 1.0E41 kg (while noting that all mass estimates are model dependent), volume V = 1.0E63 cubic meters, separation 2a = 2.44E21 meters (79 kpc), and length and width l = w = 1.0E21 meters (35 kpc). For a relative velocity between plasmas of 1000 km/sec (Shklovsky, 1960; Perola, 1981), we find Iz = 2.15E19 amperes and B-theta = mu-0*I/omega = 2.5E-8 teslas (2.5E-4 gauss)…Equating the relative velocity v to the computational distance/time quotient gives a Cygnus A time to development of 1.5E15 seconds (4.6E7 years). Thus, the entire epoch shown in Figure 2 corresponds to some 1.0E8 years while the radiation burst lasts 2.4E14 seconds (8.0E6 years). The concomitant magnetic energy is 2.5E53 joules (2.5E60 ergs) while the total simulation magnetostatic energy is 350 Arbitrary Energy Units (AEU). Thus, 1 AEU = 7.1E50 joules.”

    Note what Peratt is doing here. It’s rather subtle and it took me a while to pick up on it. He’s running his simulation in arbitrary units. Then, after the results are in he’s scaling them to match numbers from Cygnus A. So he never actually plugged in the basic parameters for Cygnus A into his calculation such as diameter, etc. He plugged in arbitrary units and then attempts to scale the results after the fact.

    “With increasing flow, the parallel Iz currents produce an attractive force between columns”

    Well, it’s well established that parallel Birkeland currents will attract each other with a strength proportional to 1/r. Antiparallel Birkeland currents will repel each other with a strength proportional to 1/r. Thus, for Peratt’s simulation to have any interaction at all the two cylinders must have parallel current, not antiparallel.

    “The total kinetic energy of the electrons during burst is 8.78E4 AEU = 6.26E55 joules (6.26E62 ergs), which yields an average energy per electron E-bar = 218 MeV.”

    Peratt has lost me here. This new statement seems to conflict with his previous statement that the electrons have energies in the range 1-10 keV. Maybe this is the energy of only certain electrons associated with the initial synchrotron burst but I don’t know.

    “The results of this research, believed to represent the largest computational study in astrophysics to date, replicate the essential features of double radio sources, peculiar, and spiral galaxies, but do not appear to be in agreement with the ‘big-bang’ creation theory of the Universe. Instead, the simulations strongly support an inhomogenous version of the Klein world model that proposes a zero-state universe consisting of magnetized plasma or ambiplasma (cf. Alfven and Klein, 1982; and the earlier references therein.”

    LOL. So Peratt says his results are consistent with ambiplasma which Anaconda rejects. He claims his results are inconsistent with the Big Bang even though his model doesn’t deal with cosmology at all.

    So to rehash, my findings concerning Peratt’s model are these:

    1.) arbitrary and unrealistic initial conditions
    2.) incorrect mass for the proton (off by 2 orders of magnitude)
    3.) Stefan-Boltzmann radiative effects not taken into account
    4.) use of arbitrary units and scaling of results afterward
    5.) statistical jitter in results caused by poor numerical modeling
    6.) inconsistent statements about electron energies

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  8. @ Tom Marking:

    Hello and welcome.

    As I indicated over at Bad Astronomy, I am no math major, so it's hard for me to directly respond one way or the other to your comment.

    But a couple of general comments seem to be in order.

    (I'm disappointed you didn't choose to respond to the scientific paper cited in this post that supports Plasma Cosmology theory. Or respond to the specific comments I already made outlining galaxy filaments, charge seperation, and double layers. Or my criticism of "dark" matter being the Atlas of the Universe even though it has never been detected.)

    You may well be right that there are imperfections in the simulation.

    That wouldn't be especially surprising considering the paper is from 26 years ago, knowledge increases over time, science advances, computers increase power and sophistication.

    I appreciate your time and effort to analyze the Peratt's paper.

    But perhaps there are more recent scientfic papers of Peratt's that can be analyzed.

    That would give more weight to your criticisms.

    By the way, what do you, Tom Marking, make of the scientific paper originally published in Astrophysical Review Letters which is the basis of this post?

    I will supply the comments that I made over at Universe Today (the comments are in the comment section of the following Oil Is Mastery post: On Predictions In Science, February 10, 2009

    Tom Marking, you have knowledge of electricity and acknowledge Birkeland currents exist between the Sun and the Earth.

    (Almost all of my interlocutors at Bad Astronomy denied the existence of electric currents in space and the nature of the Birkeland currents between the Sun and the Earth until you assured them they were electric currents. My copious offers of proof, even official news releases from NASA were not enough -- one commenter even went so far as to say NASA was crazy -- such is the strength of denial over at Bad Astronomy!)

    But you also are a believer in "black holes", "neutron" stars, and correct me if I'm wrong, "dark" matter.

    You wrote of the so-called accretion disk around a "black hole" that supposedly shoots the jets, but tell me, does anybody have as specific criteria and perameters, plus descriptions of a mechanism as Peratt offers in his paper demonstrating a simulation of an electromagnetic mechanism for galaxy formation?

    It seems people in glass houses shouldn't be throwing stones.

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  9. @ Tom Marking:

    Perhaps you'll come back, but if not then other readers should judge for themselves: I was engaged in two lengthy discussions at Bad Astronomy.

    The first discussion boiled down to whether there are electric currents in space. My interlocutors were in complete denial until Tom Marking dispelled their denial, and even then it was in the most grudging, reluctant fashion.

    The second discussion was more wide-ranging, focussing on a rather broad canvas of merits and demerits of "big bang, black hole" theory contrasted with Plasma Cosmology theory. This time you, Tom Marking, were a full participant in tone and attitude with my other interlocutors at Bad Astronomy.

    Tom Marking, you were not the worst at Bad Astronomy, and, in fact you came, here, and commented, which is to your credit. But the worst, at Bad Astronomy, are, as ever, full of passionate intensity, oblivious to the grotesque failure of their doctrine in practice.

    Their "shut my eyes to the evidence" attitude was there for all to see, like laundry hanging out on a clothes line.

    Is that what you want to be a part of, Tom Marking?

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  10. @Anaconda "That wouldn't be especially surprising considering the paper is from 26 years ago, knowledge increases over time, science advances, computers increase power and sophistication."

    That just begs the question: what work has been done by Peratt and/or others on this model during the last 26 years? Is Peratt still working on it?

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  11. @Anaconda "I'm disappointed you didn't choose to respond to the scientific paper cited in this post that supports Plasma Cosmology theory."

    I didn't find the article to be very clear on exactly what their experiment was supposed to be modeling. They talked about jets streaming out from stars. I wasn't sure what this was supposed to mean in terms of, say, our sun: the solar wind, solar prominences, solar flares, coronal mass ejection, or what not? Then they mentioned "young" stars so perhaps they're not modeling our sun at all. They zapped an aluminum disk with a high power laser thus boring a hole in it and heating up the material in the hole to plasma temperatures. Beyond that I'm not too clear on what they were attempting to model.

    So it may be worthwhile research but I just don't know.

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  12. @Anaconda "But you also are a believer in "black holes", "neutron" stars, and correct me if I'm wrong, "dark" matter."

    I'm a believer in the first two: black holes and neutron stars as long as you don't assume that black holes are a traditional point singularity as classical GR assumes (that I won't buy since there are a number of alternatives such as gravastars, etc.).

    I'm not a proponent of so called "dark matter" until such time as such exotic matter can be proven to exist experimentally. The whole notion depends heavily on how you conduct your "mass census" of a galaxy cluster and what numbers you assume for certain low-luminosity objects (e.g., brown dwarfs, etc.).

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