Question inspired by soap suds....

[tenbyfifty]

I'd nearly finished washing the dishes the other night and pulled out the inevitable teapsoon which is

always to be found in the bottom of the bowl. As I did so, my hand caused a rotation in the thin film of

soap suds left over and some rather attractive patterns started to form with one large central rotation and lots of

little swirls and eddies on the edges. Then a question popped into my head: Why is the structure of a galaxy so

simple when you consider its overall size and the amount of stuff contained in it? How come there aren't any smaller

swirls and eddies like my soap suds, or indeed a lot of other rotating phenomena found in nature?. I'm not suggesting for a moment that gravity is directly analagous to the movement of soap suds but it doesn't seem immediately obvious (to a layman) why there isn't more chaos going on in galaxies, or is it just that case that smaller substructures inside galaxies are hard

to detect?

[FLO]

Things certainly become chaotic when they collide!

[tenbyfifty]

Things certainly become chaotic when they collide!

Well yes, but as they used to say at the end of 'Tales from the Riverbank', that's another story.

[Ambermile]

So - what about planets orbiting stars then?

[tenbyfifty]

So - what about planets orbiting stars then?

Yeah but that's only a few objects orbiting a central point, whereas a galaxy contains millions of stars and they still manage to go round in a rather stately and ordered manner. A lot of natural vortex systems in nature give rise to smaller vortices but not so with galaxies. What I 'm trying to get at is, why not?

[Ambermile]

Because it's quantum Assuming that 95% of the matter in the universe is dark matter, it may well be swirling but we can't see it...

Arthur

PS - Eddies in the spacetime continuum

[tenbyfifty]

Assuming that 95% of the matter in the universe is dark matter, it may well be swirling but we can't see it...

That's interesting, but you would think dark swirling masses would still affect the motion of nearby stars.

[The Warthog]

There is movement within the stars of the galaxy. Let a few hundred thousand years go by, and the sky will be quite different. There are also things going on like the Sagittarius galaxy being torn apart within ours, and the rotation of the Milky Way is far from stately. It's like a good family - when you see it from a distance, all the turmoil is hidden beneath the surface.

Aren't the galaxies in their groups supposed to resemble bubbles?

[Astroman]

Why is the structure of a galaxy so

simple when you consider its overall size and the amount of stuff contained in it? How come there aren't any smaller

swirls and eddies like my soap suds, or indeed a lot of other rotating phenomena found in nature?.

There are a number of reasons behind these observations. The biggest ones are scale, age and distance. First of all, the structure of a galxy is anything but simple. It may appear so from tens or hundreds of millions of LY away, but if you look at the structures present in our own MW, you'll see it's very complex indeed. Based on the overall scale of the MW, at 110,000 LY across, features 1,000 LY across, such as the Tarantula Nebula nebula seem small by comparison. The Orion nebula complex is hundreds of LY across. Both of these are the result of gravitational eddies within the whirlpool of the MW. They are fresh, new eddies. Ancient eddies can be seen in the collections of stars called Globular Clusters. These formed along with the galaxy billions of years ago from just such eddies as you describe. Eddies in water streams or soap bubbles are short lived by any standard. Since one rotation of the MW takes ~200,000 years, by the time M42 reaches the other side of the galaxy, it'll probably be gone completely, leaving only a few scattered stars with similar velocities and directions. Tidal forces withing the gas will most likely form new concentrations and new star clusters etc. Ambermile's ananlogy is equally valid, but on a much smaller scale. We'd never see eddies of this size from even 2 million LY, much less hundreds of millions.

I'm not suggesting for a moment that gravity is directly analagous to the movement of soap suds but it doesn't seem immediately obvious (to a layman) why there isn't more chaos going on in galaxies, or is it just that case that smaller substructures inside galaxies are hard

to detect?

The fact is, we see chaos all around us directly related to just such eddies. Astronomers call them gravitational interacting zones or some such, because gravity runs everything, and when matter comes close to other matter, it compresses it which allows all sorts of changes in the neighborhood. It's just hard to detect from this lonely, quiet neck of the woods.

[tenbyfifty]

There are a number of reasons behind these observations. The biggest ones are scale, age and distance. First of all, the structure of a galaxy is anything but simple...

So whirlpools in soap suds are not so different from galaxies after all.

Who needs a supercomputer to model galaxy evolution when you can get bowl, some fairy liquid

and get the dishes clean at the same time.

Thanks for the reply.

[FLO]

How come there aren't any smaller swirls and eddies like my soap suds, or indeed a lot of other rotating phenomena found in nature?

As we astronomers know only too well, air is turbulent!