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Fraser
2009-Feb-11, 10:50 AM
Some of the most beautiful structures observed in the Universe are the intricate jets of supersonic material speeding away from accreting stars, such as young proto-stars and stellar mass black holes. These jets are composed of highly collimated gas, rapidly accelerated and ejected from circumstellar accretion disks. The in-falling gas from the disks, usually feeding [...]

More... (http://www.universetoday.com/2009/02/11/stellar-jets-are-born-knotted/)

iantresman
2009-Feb-12, 08:50 AM
Laboratory simulation of astrophysical jets, with pinches (knots) were identified over twenty years ago. See:

Winston H. Bostick, "What Laboratory-Produced Plasma Structures Can Contribute to the Understanding of Cosmic Structures Both Large and Small (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4316621)", IEEE TPS v14 n6 (Dec 1986)


Anthony L. Peratt, "The role of particle beams and electrical currents in the plasma universe (http://adsabs.harvard.edu/abs/1988LPB.....6..471P)", Laser & Particle Beams Vol 6 Part 3 (Aug 1988) (Online in full (http://plasmascience.net/tpu/papers.html) (PDF))

tusenfem
2009-Feb-12, 12:48 PM
Laboratory simulation of astrophysical jets, with pinches (knots) were identified over twenty years ago. See:


Indeed, such experiments were done, but you fail to see the new thing here, and that is that the knots are not pinches created by (current or flow driven) instabilities of the plasma. In the article by Ian O'Neill it is clearly written that the ejection mechanism could be totally different from what we expect, not a fire hose just spewing out plasma at a constant (or slightly varying rate) but:



According to Frank, the exciting results uncovered by the international collaboration suggest that far from being a steady stream of gas being ejected from the circumstellar accretion disk, the jets are "fired out more like bullets or buckshot." It is therefore little wonder that the vast stellar jets appear twisted, knotted and highly structured.


This is a totally different mechanism which I doubt is described in the old papers you quote.

iantresman
2009-Feb-12, 08:28 PM
From the news release (http://www.universetoday.com/2009/02/11/stellar-jets-are-born-knotted/):

According to Frank, the exciting results uncovered by the international collaboration suggest that far from being a steady stream of gas being ejected from the circumstellar accretion disk, the jets are "fired out more like bullets or buckshot." It is therefore little wonder that the vast stellar jets appear twisted, knotted and highly structured.

Bostick writes:


In 1954 [6] the author projected plasma from a small pulsed plasma gun in a direction perpendicular to a magnetic field in a vacuum of 10-5 torr. The plasma proceeded across the magnetic field in the form of tight bundles or filaments. [..] These spontaneously arising sharp-boundaried entities have been called "plasmoids. [..]

The plasma focus in the laboratory, as will be shown in the next section of this paper, generates a segmented (chopped) high-energy positive ion beam in the direction of the plasma amperian current and a high-energy (relativistic) electron beam in the opposite direction by a process which has been called the stuttering electromagnetic ram [11] (SER, sometimes called the "electronic ram"). We are nominating the SER process as a candidate for the source of the segmented gigantic galactic jets [12] -- Winston H. Bostick, "What Laboratory-Produced Plasma Structures Can Contribute to the Understanding of Cosmic Structures Both Large and Small (http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4316621)", IEEE TPS v14 n6 (Dec 1986)

Refs

[6] - W. S. Bostick, "Experimental study of ionized matter projected across a magnetic field (http://prola.aps.org/abstract/PR/v104/i2/p292_1)," Phys. Rev., vol. 104, p. 292, 1956. W. H. Bostick, "Experimental study of plasmoids," vol. 106, p. 404, 1957.

[11] - W. H. Bostick, "The morphology of the electron," Int. J. Fusion Energy, vol. 3, no. 1, pp. 45 and 68, Jan. 1985. W. H. Bostick and V. Nardi, "Electromagnetic ram as a model for production of electron and ion beams in the plasma focus and the cosmic rays and gigantic jets in the cosmos," in Proc. 19th Int. Cosmic Ray Conf., vol. 3 (La Jolla, CA, Aug. 1985), S. C. Jones, Ed. Springfield, VA: NASA Sci. and Tech. Int. Branch, 1985, p.183.

[12] - J. O. Burns and R. M. Price, "Centaurus A: The nearest active galaxy," Sci. Amer., vol. 249, no. 5, p. 56, Nov. 1983. J. 0. Burns et al., "Radio jets in classical double radio sources with strong cores," Astron. J., vol. 283, p. 515, 1984.

tusenfem
2009-Feb-13, 08:40 AM
Sorry, apples and oranges, in the new study the "buckshot" is shot out ALONG the magnetic field which penetrates through the hole in the aluminum disk, just as at a real AGN with a jet. From the paper:



Using an aluminium disk, Lebedev applied a high-powered pulse of energy to it. Within the first few billionths of a second, the aluminium began to evaporate, generating a small cloud of plasma. This plasma became an accretion disk analogue, a microscopic equivalent of the plasma being dragged into a proto-star. In the centre of the disk, the aluminium had eroded completely, creating a hole. Through this hole, a magnetic field, being applied below the disk, could penetrate through.


Whereas the experiment that you link to says:



the author projected plasma from a small pulsed plasma gun in a direction perpendicular to a magnetic field


which is totally different.