[Chaos-l] the galaxies are still turning after the March CHAOS meeting

[walter fowler]

Interesting talk about possible relationship of elliptical and spiral
galaxies (hypothesis - they may be able to change back and forth).  A key
point was raised by Margareta Thompson.  All galaxies rotate but they rotate
slowly, even on a scale of 14+ billion yrs (the accepted "age of the
universe).  Therefore interaction between galaxies that involves the
relative rotations seems to be temporally constrainted.  I looked up some
numbers in a recent book (not on line):  our Sun makes an orbit around the
Milky Way in about 225 million years and something on the edge of the Milky
Way "would take even longer" (this is not intuitively obvious).  The same
book says both that the Milky Way "started to form" 13+ billion yrs ago and
the universe is 14 billion yrs old.  Assuming that these numbers are in the
right ballpark, the Milky Way couldn't have rotated more than a few dozen
times in its history.  This is pretty different than what was shown in the
computer simulations of rotating, interacting galaxies!  So we should all
take heed to the old saying:  you only go around once!
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