Dark Matter vs. Magnetism

[ccwebb]

I just watched an amazing episode of "How the Universe Works", season 4 episode 1: Forces of Mass Construction.

 

The episode was discussing the role of magnetism in the universe, and how it is a lot more than previously thought. There was a portion where astronomer Dr. Phil Plait stated that the shape of the Milky Way's arms are due to magnetism. Then they showed this special effects how magnetism actually prevents and creates star formation.

 

However, I thought dark matter is the reason why galaxies don't fly apart and forms stars.

 

 

So, is the theory of dark matter starting to disappear due to the discovery of magnetism on the galactic level?

[swansont]

Since that episode is paywalled, can you give a more complete summary of what was said? Your current synopsis is very vague. Not knowing what was presented basically makes it impossible to address your concern.

 

AFAIK, dark matter is not being replaced by magnetism

[ccwebb]

Something along the lines of:

 

Due to angular momentum, dust clouds are not suppose to condense into stars; The gravity isn't strong enough. However, when the magnetic field is examined of the charge dust particles a different picture comes to play. The magnetic field would be strong enough to pull the particles closer together, thus helping gravity in this case.

 

The part with Dr. Plait was pointing out is that magnetism is responsible for keeping the spiral arms of galaxies together. Since there isn't enough visible mass to keep everything where it is, researchers looked into magnetism. They found where the magnetic field concentrated at, the dust and other material would stay there...thus an arm of the Milky Way.

[Strange]

Due to angular momentum, dust clouds are not suppose to condense into stars; The gravity isn't strong enough. However, when the magnetic field is examined of the charge dust particles a different picture comes to play. The magnetic field would be strong enough to pull the particles closer together, thus helping gravity in this case.

 

That sounds plausible.

 

The part with Dr. Plait was pointing out is that magnetism is responsible for keeping the spiral arms of galaxies together. Since there isn't enough visible mass to keep everything where it is, researchers looked into magnetism. They found where the magnetic field concentrated at, the dust and other material would stay there...thus an arm of the Milky Way.

 

I haven't come across this before. I sounds like a reference to this research: https://public.nrao.edu/news/pressreleases/galaxy-magnetic-field

"Astronomers making a detailed, multi-telescope study of a nearby galaxy have discovered a magnetic field coiled around the galaxy's main spiral arm. The discovery, they said, helps explain how galactic spiral arms are formed. The same study also shows how gas can be funneled inward toward the galaxy's center, which possibly hosts a black hole."

 

So, even if the magnetic fields have a role in the formation of the spiral arms, this is quite different from the role of dark matter, which is related to the orbital speed of stars and dust at various distances from the centre. This is independent of the structure of the arms. And is also required to explain the relative motion of galaxy clusters.

[Bill Angel]

The existence of dark matter has been confirmed by the phenomena of "gravitational lensing". Astronomers can estimate the amount of dark matter contained in a galactic cluster by how much the light of more distant galaxies is distorted by passing near the cluster.

 

See Galaxy clusters and gravitational lensing

 

This estimate of the amount of dark matter present would still remain valid even if magnetic effects played a role in galactic dynamics and spiral arm formation.

Edited October 14, 2015 by Bill Angel

[ccwebb]

I am not debating the existence of dark matter. I am wondering if the amount of dark matter is correct. The amount is based on calculating how fast the outer stars are orbiting their galaxy and what mass is required to hold them in place.; Galaxy rotation curve. (It is also calculated by the amount of gravitational lensing.)

 

So, if magnetism is helping hold stars in place while they whip around a galaxy, then shouldn't that reduce the amount of calculated dark matter?

[swansont]

So, if magnetism is helping hold stars in place while they whip around a galaxy, then shouldn't that reduce the amount of calculated dark matter?

 

But you haven't established that this is happening. Since magnetism drops off faster than gravity, it should have the opposite effect than what we see from dark matter — a greater effect near the center, rather than further out.

[acsinuk]

The WMAP results state 4.6% actual matter and 24% dark matter. So to balance the galaxies we need an attractive magnetic force of five times that of mass attraction force.

[ccwebb]

 

But you haven't established that this is happening. Since magnetism drops off faster than gravity, it should have the opposite effect than what we see from dark matter — a greater effect near the center, rather than further out.

True, but the show countered this point by stating that EACH dust particle has becomes charged due to... solar winds, super novas, etc... Now the magnetism doesn't have to go as far, just to the next charged particle.

 

Does that make sense? (Please forgive me if my verbiage is incorrect. I am trying to quote the show, and I am not a scientist myself. Just highly fascinated with it though!)

[swansont]

True, but the show countered this point by stating that EACH dust particle has becomes charged due to... solar winds, super novas, etc... Now the magnetism doesn't have to go as far, just to the next charged particle.

 

Does that make sense? (Please forgive me if my verbiage is incorrect. I am trying to quote the show, and I am not a scientist myself. Just highly fascinated with it though!)

 

Not really. If you have charged particles moving at the same speed, they don't see a magnetic field from each other. They're at rest in their own frame.

[ccwebb]

I found the episode on youtube:

 

https://www.youtube.com/watch?v=oq_pZub-QTc

 

Please note time stamps:

8:16 Begins the sections about forming stars

9:25 the statement "..gravity is alone is not enough"

9:43 Talks about angular momentum.

 

15:57 it begins talking about galactic magnetic fields

20:42 & 24:36 It refers to energy waves moves through dust clouds creating magnetic fields.

[swansont]

Star formation is moot, simce dark matter was never a proposed issue in forming them, AFAIK.

 

You might notice then whenever anyone clarifies what the mean by "big" magnetic fields, they say they mean spatially big. They never mention how strong the fields are, except in vague terms.

[acsinuk]

The magnoflux hypothesis states that each galaxy is magnetised in a set direction by an induced magnetic field in the central hub AKA a super massive black hole. This is probably what spins the galactic arms they are talking about

[Strange]

The magnoflux hypothesis states that each galaxy is magnetised in a set direction by an induced magnetic field in the central hub

 

Is this hypothesis your own idea? If so you shouldn't be bringing it up in the science sections of the forum.

 

This is probably what spins the galactic arms they are talking about

 

It doesn't appear so. Wishful thinking?

[Phi for All]

The magnoflux hypothesis states that each galaxy is magnetised in a set direction by an induced magnetic field in the central hub AKA a super massive black hole. This is probably what spins the galactic arms they are talking about

 

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Moderator Note

Please don't introduce your pet theories into topics in the mainstream sections. They aren't well-enough supported for those who are looking for our current best explanations. I hope you aren't purposefully trying to make students fail their tests.

 

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