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transfer of angular momentum during protostar collapse?



At 03:36 PM 2/20/98 -0400, Ludwick Kowalski wrote:


I've been watching this thread, hoping someone more eloquent would respond,
but ...

I have another question for those who teach astronomy. The first
question (how is solar spinning angular momentum transferred to the
revolving planets via magnetic forces?) was not answered. I assume
it is not a simple topic.


This is the present situation. According to nebular models, as stated by
Zeilik (chapter 12, 8th edition) the initial distribution of angular
momentum must have been just the opposite to what we now have. Just think
about the contracting cloud of gas (with a fixed spin) which becomes a
flat disk, more or less. The central part has the highest mass and the
largest share of angular momentum. As I am thinking about this again I
realize this is not at all obvious. But that is what the author wrote.
If the young solar system had a different distribution of angular
momentum than now then we do have an intersting topic. Zeilik claims
that the magnetic field can do the transferring.

That it can has been claimed for many years - I remember hearing
discussions of this at Protostars and Planets II way back in 1984. Indeed,
the mechanism has great intuitive appeal. The magnetic field couples to
the plasma in the accretion disk, and "somehow" transfers angular momentum
outward while mass moves inward.

Something must do this, since the present solar system has most of the
angular momentum in the outer planets (lots of it in rotation rather than
orbital motion) while virtually all the mass is in the Sun.

I haven't followed this work in detail, but my sense is that the underlying
mechanisms which might accomplish this are still not well-understood.
Other researchers at the time were invoking another not-well-understood
mechanism ("viscous turbulence") even though there were no good
mathematical descriptions of turbulence, either.

Also, on Ludwick's question concerning circularization of orbits - recent
extra-solar planets appear to be in all sorts of eccentric orbits, so the
ubiquity of nearly-circular orbits may be an anomaly of our neck of the cosmos.

George Spagna **********************************************
Department of Physics * *
Randolph-Macon College * "I like to keep an open mind, *
P.O. Box 5005 * *
Ashland, VA 23005-5505 * but not so open my brains fall out." *
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phone: (804) 752-7344 * - Arthur Sulzberger *
FAX: (804) 752-4724 * *
e-mail: gspagna@rmc.edu **********************************************
http://www.rmc.edu/~gspagna/gspagna.html