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Why can't the neutrino be dark matter?


dimreepr
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31 minutes ago, dimreepr said:

Couldn't an extremely large concentration of neutrinos, for reason's unkown, explain the observations that leads to dark matter?

Perhaps there are regions in space that trap's neutrinos, like a black hole does with light? 

How would they be trapped? You’d need a black hole, or a neutron star very close to the BH limit, to trap them gravitationally.

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28 minutes ago, swansont said:

How would they be trapped? You’d need a black hole, or a neutron star very close to the BH limit, to trap them gravitationally.

I guess, he meant that they slowed down from their initial relativistic velocity to the frame of reference of the surrounding galaxy, so they are barely moving, only just as much as the entire galaxy in which they remain.

 

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2 hours ago, Sensei said:

I guess, he meant that they slowed down from their initial relativistic velocity to the frame of reference of the surrounding galaxy, so they are barely moving, only just as much as the entire galaxy in which they remain.

 

If they were massless, this would be moot. With a mass of less than an eV, non-relativistic is pretty slow. How do they slow down?

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From my limited understanding, the reason "run of the Mill" neutrinos have been excluded from the list of candidates for making up a major component of dark matter is that it would have altered the formation of the universe.  That many neutrinos would have prevented the small scales structures from forming as early as they did.

That doesn't mean neutrinos are out of the question entirely, there is the hypothesized "sterile" neutrino, which doesn't interact with other matter at all, except gravitationally. Some recent findings have suggested to its actual existence.

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On 10/21/2022 at 12:55 PM, swansont said:

How would they be trapped? You’d need a black hole, or a neutron star very close to the BH limit, to trap them gravitationally.

I was pondering that perhaps, quantum wormholes could recirculate them into the same region of space.

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  • 2 weeks later...

My thinking is that if neutrinos where the "dark matter" they would be more concentrated near the centre of the galaxies but this is not the required mass distribution for "dark matter".

I looked for the required distribution of "dark matter" within galaxies and I found an article from Britannica explaining this: (https://www.britannica.com/science/dark-matter).

It says: "In general, the speed with which stars orbit the centre of their galaxy is independent of their separation from the centre; indeed, orbital velocity is either constant or increases slightly with distance rather than dropping off as expected. To account for this, the mass of the galaxy within the orbit of the stars must increase linearly with the distance of the stars from the galaxy’s centre. However, no light is seen from this inner mass—hence the name “dark matter.”"

So, a linearly increase of mass with with the distance from the centre is required. I find this very strange, too strange. "Dark matter" is something too strange for my mind...

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