Nature's demo of: the "right hand rule" (magnetics)

Post #1,797 by Ashton 7/14/01 2:49:25 AM Reply	Nature's demo of: the "right hand rule" (magnetics) Talk 'bout yer Billion Terawatt light shows.. Even with handy sci- exponential notation, we cannot imagine the scale here: we just think that.. a glance at the exponent is the same as actually comprehending such magnitudes. Kinda places 'Billy Gates' or maybe North America in some sort of perspective - if not quite the 50K or so Terran 'years' of homo-sap's temporary lease (perhaps near cancellation -?- for wrecking the furniture and annoying the neighbors with perpetual soap opera broadcasts) (They can relax a bit - at least we aren't likely to drop in unannounced for a visit, dropping our urine bags on their turf) A.
Post #1,947 by deSitter 7/16/01 4:42:20 PM Reply	Re: Nature's demo of: the "right hand rule" (magnetics) ? Where?
Post #1,964 by Ashton 7/16/01 6:47:26 PM Reply	Merely my association.. of the juxtaposed ~90\ufffd axes And absolutely everything noticed by mind IS 'via association' or it is missed entirely. (Then we construct the metaphors yada..)
Post #2,054 by deSitter 7/17/01 12:02:19 PM Reply	OK Actually there is a RHR issue, since some people think the formation of stars and spiral arms is associated with galactic magnetic fields.
Post #2,107 by pwhysall 7/17/01 5:37:40 PM Reply	Question Barred spiral galaxies. What's up with that? How do the bars exist without just blurring into the spiral shape? Please, my mathematics is feeble. Keep any answer simple enough for me to understand :) -- Peter Shill For Hire
Post #2,180 by Another Scott 7/18/01 6:41:07 AM Reply	An explanation is here. [link\|http://www-thphys.physics.ox.ac.uk/users/SimonBerman/gasdyn.html\| [link\|http://www-thphys.physics.ox.ac.uk/users/SimonBerman/gasdyn.html\|http://www-thphys.p.../gasdyn.html]] From spectroscopic Doppler shift measurements, the bar structure is observed to rotate as a solid body in the same sense as the galaxy about an axis normal to the plane of the disk. This is unlike the differential rotation seen in the main body of the disk. The axial ratios of bars vary from one when a bulge is present without a bar up to about five, whereas the actual shape of a bar is better described as boxy than elliptical. From observing bars in edge on galaxies it is known that bars are a three dimensional phenomena with thickness generally larger than that of their host galaxy. Given that bars are so common, it seems safe to assume that they are both easy to 'make' and fairly long lived structures. Numerical simulations have shown that bars can form in one of two ways, either spontaneously through global instabilities in an unbarred disk galaxy or induced by a close interaction with a companion galaxy. Once formed, bars can have a significant effect on the evolution of the host galaxy, channeling gas flows into the galactic nucleus to ignite starbursts or AGN's or feeding a central black hole. [...] But bars probably do not live for ever. Although a pure stellar bar seems, in simulations, to remain robust for a Hubble time or more, the accumulation of large quantities of gas at a bar's centre can lead to its disruption, by modifying the orbit's of the constituent stars. This could happen if the host galaxy swallowed a satellite galaxy or it could be the result of the gas flows mentioned above. So it seems to be caused by a gravitational effect and isn't stable forever but is for a rather long time. (A [link\|http://www.astro.virginia.edu/~jh8h/glossary/hubbletime.htm\|"Hubble Time"] is the inverse of the Hubble Time Constant and is the estimated age of the universe (assuming uniform expansion)). HTH. Maybe deS can elaborate. Cheers, Scott.

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