From: dseeman@novell.com (Daniel Seeman)
Subject: Re: Dark Matter
Organization: Novell Inc., San Jose, Califonia
Date: Fri, 18 Dec 1992 22:35:17 GMT

In article <1992Dec18.212209.24526@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>
>     I just read a rather interesting article in Nature that suggests
>     that the rotation curves of gas orbiting spiral galaxies can
>     be explained by magnetic stresses (Battanger, /etal 
>     Nature, 360:613 (1992), News and Views p. 624 of the same issue).
>  
>     From the News and Views portion (by J. Binney), the main argument goes
>
>           ... by arguing that tens of kiloparsecs from the center
>           of a galaxy, where the gas density is usually very low, the
>           dynamics of the gas may be strongly affected by a magnetic
>           field of 1 picotesla.  We know that the interstellar
>           field tends to wind around galactic disks, so that to a first 
>           approximation one can imagine that the field lines form a
>           series of gas-filled hoops within the plane of the disk.
>           The magnetic field B imposes two kinds of forces on the
>           hoop; a tension 1/2 B^2/\mu_0 runs the long way around the
>           hoop, pulling it more snugly around the galaxy, while in
>           the two perpendicular directions, the field exerts pressure
>           1/2 B^2/\mu_0, tending to cause the hoop to fatten into
>           a doughnut.
>
>           The magnetic tension in the hoop must be counteracted by
>           some combination of a net outward force on the hoop due
>           to a radial gradient in the perpendicular magnetic pressure,
>           and an excess of the centrifugal force on the spinning
>           hoop over the inward gravitational pull of the galaxy.
>
>     In any case, Battinger \etal use M31 to show that the rotation
>     curves would be satisfied if there is a field of about 0.8 picotesla
>     between 10 and 30 kiloparsecs.  Apparently observations of 
>     synchrotron emission are being used to claim that the field strength 
>     is correct for this mechanism in M31.  However, from our own galaxy at 
>     our position the component of the magnetic field along the azimuthal
>     direction is roughly four times smaller than 0.8 picotesla.  So, at
>     our position, magnetic forces would be about an order of
>     magnitude smaller than necessary for their mechanism to work.
>
>     Anyway, it is an interesting paper.
>
>                              dale bass
>-- 
>C. R. Bass                                          crb7q@virginia.edu        
>Department of Mechanical, 
>     Aerospace and Nuclear Engineering
>University of Virginia                              (804) 924-7926

Hi,

In school, I was fortunate enough to "rub elbows" with a man named Joel Primack
(sorry Joel if I misspelled your name...).  He was very interested in the
subject of Dark Matter.  Joel has probably studied this effect (and for all we
know, he may be a member of the /etal group).  At any rate, Joel works at the
Univ. of Calif @ Santa Cruz.  Just for kicks, you might give him a call.
He will probably have some interesting insights on this article...

Just thought you might like to know...

dks.
Newsgroups: sci.physics,alt.sci.physics.new-theories