How Do Spiral Galaxies Maintain Their Shape?

[twofu]

So I was watching this:

which talks about the winding paradox of spiral galaxies, e.g. the stars all move at the same relative speed however that shape is maintained. However, we still have those shapes.
The video talks about density waves of some sort. I don't really understand. This can't be some sort of probability density coming from wave amplitude like in quantum mechanics, or is it?

Anyone care to elaborate or if you have your own explanation?

Thanks!

 

[IsometricPion]

The video talks about density waves of some sort. I don't really understand. This can't be some sort of probability density coming from wave amplitude like in quantum mechanics, or is it?

You are correct, it has nothing to do with quantum mechanics. Unfortunately I do not know much more on this topic than is in that video and on the http://en.wikipedia.org/wiki/Density_wave_theory" . The wikipedia page has several animations that help demonstrate some of the ideas you heard about in the video.

 

[Chronos]

The short answer is [believed to be] spiral density waves. See
http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT423/HTML/AT42305.htm#Anchor-spiral-32084

 

[twofu]

Thanks for the sources, it helped a lot :)

 

[Astro.padma]

The new supercomputer simulation's might help you as well. Go through this , where the spiral arms of the milky way galaxy has got an explanation for it's spirality.

http://astronomylatest.blogspot.com/2011/09/simulation-answers-questions-about.html?spref=fb

 

[Dotini]

From the desk of NASA scientist Tony Phillips comes this rather astonishing article on the discovery of a star - not a galaxy - with spiral arms. If, how or why the physics of this phenomenon relates to that of galaxies is not for me to say.
http://science.nasa.gov/science-news/science-at-nasa/2011/31oct_spiralarms/

Respectfully submitted,
Steve

 

[Said Harbieh]

Yeah that star with the spiral arms is very interesting, i would like to see more pictures of it :S