Are EM forces responsible for galactic structures?

[TakenItSeriously]

I have seen a couple of references on EM forces creating galactic structure such as spiral arms and perhaps even intergalactic structure such as galactic filaments.

 

https://public.nrao.edu/news/pressreleases/galaxy-magnetic-field

Or in the documentary:

"The Universe Forces of Mass Construction"

 

But, it seems to me that a structure such as a spiral arm should explain the velocities.

 

Imagine EM forces tying the SMBH to stars in a spiral arms, and every star in each arm connected in a lattice work of EM forces creating a semi-rigid spiral arm structure. Then you would expect the same kind of swept back arm that we see. Then the structure, in turn would create a compliance force that should account for the added motion of the stars.

 

On the other hand gravity alone doesnt make sense. Imagine we added enough brown dwarfs in a perfect radial distribution that was the opposite from the radial distribution of visible stars to explain the flat velocity curve.

 

Then the velocities would make sense but the galactic structures wouldnt. Even if they formed arms for some reason, which would seem rather bizaar, they wouldnt be swept back, they would be spokes, because there wouldn't be any kind of resistance force to cause it.

 

I could see gravity creating a smooth disk, belts, rings or clustering into BHs like asteroids created the planets, but it's hard to imagine why gravity would create most of the structures like those found in Galaxies.

 

Perhaps this is also why we don't see DM effect planets. While the stars all have strong EM fields, the planets have relatively weak or no fields and em fields wouldnt effect the motions of planets.

 

We didnt know EM forces existed at a galactic scale when DM was calculated and couldn't have taken those forces into account. So with gravity plus structure, it seems like there is no need for DM.

 

So the question is could EM forces be strong enough to form spiral arms in a galaxy if given enough time?

Edited June 26, 2016 by TakenItSeriously

[Strange]

This isn't a subject I know a lot about (it is very complex) but a couple of points:

 

1. The stars are not "locked" into the structure of the arms. They move in and out of them. The arms are just areas of higher density of gas and stars (this means they are also areas of higher star formation so there are more young, bright stars there, making the arms more visible). It is a bit like when you get cars bunched up on the highway: individual move through the area of congestion even though the congested area stays still (or moves backwards).

 

2. The arms are not "swept back" but actually curve in the direction of rotation.

 

3. Electromagnetic forces may have a role (particularly in keeping the ionised gas in place) but it will be much smaller than the gravitational effect.

[Mordred]

Actually because EM radiation falls off in strength the universe and even most galaxies are considered electromagnetically neutral. Even a magnetars electromagnetic influence isnt felt at any significant stellar distance.

 

How galaxies form into its stellar formation is a combination of gravity, rotation and whats called density waves.

 

The spiral arms are in a sense misleading. Those are simply regions where the stars are brighter than the stars between the arms which are extremely difficult to see. The stars inside the arms are typically younger stars.

 

For an analogy we will simplify how density waves work. You do this at home.

 

Take a tub of water. Place in that tub semi buoyant particles doesnt matter what you use. Now start stirring the water in the same continous direction (circular).

 

The water will form a whirlpool. The particles will flatten out and follow the whirlpool path.

 

The same density waves work on both galaxy rotation for spiral galaxies as well as tbe rings of Saturn.

https://en.m.wikipedia.org/wiki/Density_wave_theory

Edited June 26, 2016 by Mordred

[swansont]

Imagine EM forces tying the SMBH to stars in a spiral arms, and every star in each arm connected in a lattice work of EM forces creating a semi-rigid spiral arm structure. Then you would expect the same kind of swept back arm that we see. Then the structure, in turn would create a compliance force that should account for the added motion of the stars.

 

Instead of imagining, what science does is model it instead. You can imagine things that aren't physically possible.