Thread: Does charge affect the rotational curve of a galaxy?

Electricity is currently the most fascinating area of physics for me, but it's my biggest weakness too. I tend to misunderstand some of the concepts. So, I'm not entirely sure if this is correct.

I've mentioned in some other threads how I think that near the center of gravity of a large object, where the gravitational force is strongest, we could expect a higher than normal concentration of protons, because the gravitational force makes it so you need fewer electrons to hold the protons together. (It does this for electrons too, making them not need protons as much, but less so because they are less massive.)

So, near the center of a galaxy, it seems reasonable that there would be a greater positive charge. Gravity there is strong enough to overcome the electric repulsion. Then the negative electric charges could accumulate toward the outer regions, where there is a lot more room for it. The positive core still acts on them, at least weakly, and the negative charges act on each other weakly because they've got so much room.

In a situation like that, if the outer region were to spin faster or slower (in terms of radians) than the inner core, I think that would generate a magnetic field wouldn't it? ..... But the outer region does not spin faster or slower than the inner core. The rotational curve is flat. Maybe that's because a state that leads to generating a magnetic field is a higher energy state than one that does not?

Originally Posted by kojax

So, near the center of a galaxy, it seems reasonable that there would be a greater positive charge. Gravity there is strong enough to overcome the electric repulsion. Then the negative electric charges could accumulate toward the outer regions, where there is a lot more room for it. The positive core still acts on them, at least weakly, and the negative charges act on each other weakly because they've got so much room.

No, this is not reasonable.

Why on earth would you think so ?

Originally Posted by DrRocket

Originally Posted by kojax

So, near the center of a galaxy, it seems reasonable that there would be a greater positive charge. Gravity there is strong enough to overcome the electric repulsion. Then the negative electric charges could accumulate toward the outer regions, where there is a lot more room for it. The positive core still acts on them, at least weakly, and the negative charges act on each other weakly because they've got so much room.

No, this is not reasonable.

Why on earth would you think so ?

Partly, I am taking the behavior of protons and electrons in a uniform sphere and extrapolating it. I'm pretty sure the negative charge tends to settle toward the outside.

I guess it depends on how things balance. Gravity exerts a stronger force on protons than it does on electrons (because of their greater mass), but if everything is in a stable orbit, then gravity isn't playing much of a role in the distribution of charge, and electrical forces dominate it. In that case charge should be evenly distributed. However, if gravity does start to play a role, then protons will begin to resist their mutual repulsion against each other to a greater degree than electrons do, because they are "heavier" inside of a gravitational field. That means that a good balance between attractive and repulsive forces is found at a nearer radius for protons than for electrons. At a nearer radius, they're clumped tighter together (because there is less physical area for them to occupy at that radial distance than there is at further radial distances), but gravity is also stronger. At further radius's they don't have to get as close to each other to fit.


If there are two forces acting upon the same object along the same vector, then it's easier just to treat the two forces as though they were single composite force, and model things that way.

The gravity+electric force pulling protons & electrons together is opposed by the purely electric force pushing them apart. At some optimal distance, those two forces will always balance, but if the gravity+electric force is stronger, that balance will be achieved at a nearer distance than it would be if the gravity+electric force were weaker.

Originally Posted by kojax

Originally Posted by DrRocket

Originally Posted by kojax

So, near the center of a galaxy, it seems reasonable that there would be a greater positive charge. Gravity there is strong enough to overcome the electric repulsion. Then the negative electric charges could accumulate toward the outer regions, where there is a lot more room for it. The positive core still acts on them, at least weakly, and the negative charges act on each other weakly because they've got so much room.

No, this is not reasonable.

Why on earth would you think so ?

Partly, I am taking the behavior of protons and electrons in a uniform sphere and extrapolating it. I'm pretty sure the negative charge tends to settle toward the outside.

I guess it depends on how things balance. Gravity exerts a stronger force on protons than it does on electrons (because of their greater mass), but if everything is in a stable orbit, then gravity isn't playing much of a role in the distribution of charge, and electrical forces dominate it. In that case charge should be evenly distributed. However, if gravity does start to play a role, then protons will begin to resist their mutual repulsion against each other to a greater degree than electrons do, because they are "heavier" inside of a gravitational field. That means that a good balance between attractive and repulsive forces is found at a nearer radius for protons than for electrons. At a nearer radius, they're clumped tighter together (because there is less physical area for them to occupy at that radial distance than there is at further radial distances), but gravity is also stronger. At further radius's they don't have to get as close to each other to fit.


If there are two forces acting upon the same object along the same vector, then it's easier just to treat the two forces as though they were single composite force, and model things that way.

The gravity+electric force pulling protons & electrons together is opposed by the purely electric force pushing them apart. At some optimal distance, those two forces will always balance, but if the gravity+electric force is stronger, that balance will be achieved at a nearer distance than it would be if the gravity+electric force were weaker.

The electric force among protons and electrons dwarfs gravity. Your analysis doesn't hold water. Gravity only becomes a factor when masses are large and any net charge is small -- which is exactly whan happens in the case of galaxies.

Do you really think that all the astrphysicists on the planet would overlook the electric force if it were really a big player in galactic structure ?

Originally Posted by DrRocket

The electric force among protons and electrons dwarfs gravity. Your analysis doesn't hold water. Gravity only becomes a factor when masses are large and any net charge is small -- which is exactly whan happens in the case of galaxies.

Even if it dwarfs it (which it does), the effect should still occur somewhat. There would be a slightly bigger concentration of positive charge toward the center, because the number of electrons required to keep the protons close to each other is still smaller by that very small amount.

The question is whether it can become a chain reaction..... of sorts. Suppose you have two rings, one inside the other, with slightly different charges, and they're spinning at different rpm. If that results in a net magnetic field, then I'm wondering if maybe that field would cause charge to continue to migrate? Maybe the charge keeps migrating until a certain equilibrium is reached, and that equilibrium is the point where the two discs are rotating at the same RPM as each other.

...... so it's kind of a rough hewn hypothesis. I don't know if that would really happen or not.

Do you really think that all the astrphysicists on the planet would overlook the electric force if it were really a big player in galactic structure ?

I'm really not impressed by arguments to consensus. Of course it is possible for a large group of people (even very smart people) to arrive at an inaccurate conclusion together or miss something. How do you think the world got religion?


Why do you think it took over 2000 years after the invention of writing for humanity to think of the printing press? Clearly a lot of very smart people were looking at that problem for a very long time and missing something obvious.

Originally Posted by kojax

Even if it dwarfs it (which it does), the effect should still occur somewhat. .

OK. Suppose that there is a single extra proton near the center of some galaxy. So what ?

Scale is everything. "somewhat" is meaningless.

Originally Posted by DrRocket

Originally Posted by kojax

Even if it dwarfs it (which it does), the effect should still occur somewhat. .

OK. Suppose that there is a single extra proton near the center of some galaxy. So what ?

Scale is everything. "somewhat" is meaningless.

I'm thinking that if the separation were enough to create a magnetic field, that magnetic fields push protons in the opposite direction than electrons, so if the field pointed in a direction that tended to push electrons outward, then that same field would tend to push protons inward.

So the sequence of time is:

1) a galaxy without a flat rotation curve (one that has the rotation curve we would normally expect, like in the solar system) experiences a small amount of charge differentiation, where the outer regions become slightly negative and the inner regions become slightly positive.

2) The difference in rotational period between the inner and outer regions creates a magnetic field.

3) The magnetic field causes further charge migration.

4) The magnetic field becomes stronger, causing even more charge migration.

5) This becomes a feedback loop, which continues until the combination of electric and magnetic forces is great enough to flatten the rotation curve.

6) Once the rotation curve is flat, the magnetic field disappears, and we're left with only the charge differentiation.


That's the thing about feedback loops. If you have a sensitive enough microphone, and you put it near enough to the speaker, then the sound of a fly rubbing its legs together can emit an ear piercing shriek.

Originally Posted by kojax

Originally Posted by DrRocket

Originally Posted by kojax

Even if it dwarfs it (which it does), the effect should still occur somewhat. .

OK. Suppose that there is a single extra proton near the center of some galaxy. So what ?

Scale is everything. "somewhat" is meaningless.

I'm thinking that if the separation were enough to create a magnetic field, that magnetic fields push protons in the opposite direction than electrons, so if the field pointed in a direction that tended to push electrons outward, then that same field would tend to push protons inward.

So the sequence of time is:

1) a galaxy without a flat rotation curve (one that has the rotation curve we would normally expect, like in the solar system) experiences a small amount of charge differentiation, where the outer regions become slightly negative and the inner regions become slightly positive.

2) The difference in rotational period between the inner and outer regions creates a magnetic field.

3) The magnetic field causes further charge migration.

And the charge migration creates a HUGE opposing electric field.

This is why nearly all plasmas are quasi-neutral.

Your idea won't work. Give it up. You are going down a blind alley.

Originally Posted by DrRocket

And the charge migration creates a HUGE opposing electric field.

This is why nearly all plasmas are quasi-neutral.

Your idea won't work. Give it up. You are going down a blind alley.

That is true... unless the electrons were also speeding up in their orbits as they migrated outward (and the protons slowing down as they migrated inward.) But unfortunately for my hypothesis, it doesn't make sense for that to happen.

If anything, the protons and the electrons would both be slightly slowed if they were raised or lowered by a magnetic field, because the cross product of their velocity and the magnetic field would point slightly against the direction of their orbits during the transition. For the protons that would benefit the model, but.... not for the electrons. (And it would be a very small benefit at that.)

So, now I've been reexamining this. Clearly you are right that the feedback effect I was thinking about is self terminating. It would stop once the charges become sufficiently polarized to counter the magnetic field.


However, some polarization should still be present due to gravity (exerting a stronger pull on protons than electrons), and in a system with unevenly distributed rotational curves that would create a magnetic field. The question is how strong would that field be, and what does it do?

Centripetal force is the key. If the magnetic field can slow down the protons and accelerate the electrons, then the centripetal forces will oppose gravity by different amounts than they did before. If the protons toward the middle orbit slower than they should, and the electrons on the outer edge orbit faster than they should, that both 1) - Creates a flatter rotational curve, and 2) - Opposes the electric force.