Quote:
Originally Posted by renormalised
You also get moving density waves in galaxies as well, something I forgot to mention.
These also do the same thing as material passing in and out of standing waves....gets compressed and forms spiral arms.
The spiral arms are actually all those OB associations and HII regions, along with the other dust and gas. They are just areas of over density...roughly 10-20% higher than the surrounding space. They travel a lot slower than the general rotation of the galaxy's contents and that's why the arms appear as they do.
Gravity does play a roll....it does all the jostling about of the stars and gas, starts the formation of the stars by collapsing the gas and dust clouds etc.
http://burro.cwru.edu/Academics/Astr...al/spiral.html
http://nedwww.ipac.caltech.edu/level.../carlberg.html |
Thanks Carl. Absolutely amazing !
Just read thru both links for the first time. Will read them again a few more times to get it to sink in. The last paragraph on the second link, (a better paper), contains a nice 'bottom-line' summary:
"In the end a complete theoretical description of all the details of spiral patterns will involve a tremendous amount of complicated physics of stars, gas, magnetic fields, and gravity. A very good approximate description of spiral structures is a description of many stars moving about as described by Newton's dynamics and theory of gravity. Stars moving together in nearly circular orbits are strong amplifiers of regions of higher star density, and they create the visible trailing spirals that we observe."
Cheers
PS: If I purchased, read, assimilated and understood all of the text books you have pointed me at over the last few weeks, apart from being brain-dead, I'd be a starving, broke, all-knowing, fully indoctrinated, card carrying Cosmologist !! Can't have that now ! There's too many of those guys .... and their theories .. phooey !!
but, then again, ... I might just try ...
