Dark matter musings

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I have some questions about dark matter. My understanding is that one of the pieces of evidence for dark matter is the rotation of galaxies. The galaxies look almost like they are solid objects, in that, the outside of the galaxies are rotating almost as fast as the inner areas of the galaxies.

I have also read that dark matter appears to be in the form of a roughly spherical halo around galaxies.

This leads me to a conclusion, which frankly, my be obvious or silly, I can’t really determine which…

Dark matter maintains a spherical shape which is quite unusual for normal matter – it should flatten to a disk. The possibilities that jump out at me are that dark matter did not start off with any angular momentum therefore it does not rotate but is instead rather static. That seems unlikely. So there is another possibility which is that the dark matter halo is actually a ‘solid’, if you will. That of course implies that while the dark matter only very weakly interacts with normal matter, it does interact with other dark matter – forming some sort of lattice. That would account for the rotation of the galaxy; if it was impeded in a solid rotating matrix of dark matter.

Another thing that has always bothered me is the motion of globular clusters. These little odd balls orbit the center of the galaxy but not in the plane of the galaxy – they form a halo of sorts around the galactic center. I can’t even find a explanation of why they exist. I mean why are they so special that they get to buck the trend of moving in the galactic plane. Is there a hypothetical tie in to dark matter and globular clusters? Are they a result of higher density dark matter moving through lower density halo?

Well, like I said all this may be silly and actually belong in the unexplained, but I am counting on some of the physicists and astronomers out there to add a bit of ‘class’ and reality to the discussion. :)
 
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MeteorWayne

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Maybe I can help a little. What causes a sphere to change into a disk is nongravitational forces, like friction, EM absorbtion and radiation, etc. Since DM has none of that, it follows pure gravitational (Newtonian, more or less) paths.

Regarding globular clusters, it is believed they may be the remnants of small galaxies that were stripped of most of their mass and gas during the process of being "eaten" by the more massive galaxy.

Hope that helps.

MW
 
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MeteorWayne":dq8um38h said:
Maybe I can help a little. What causes a sphere to change into a disk is nongravitational forces, like friction, EM absorbtion and radiation, etc. Since DM has none of that, it follows pure gravitational (Newtonian, more or less) paths.

I never realized that I just thought the disk was a result of angular momentum - I will have to research that to understand it better - thanks.

Regarding globular clusters, it is believed they may be the remnants of small galaxies that were stripped of most of their mass and gas during the process of being "eaten" by the more massive galaxy.

The motion and the physical makeup of globular clusters still just seems odd to me.
 
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MeteorWayne

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Well other small galaxies that get stripped and absorbed are approaching at random speeds and angles, so you would expect the remaining cores to also be randomely distributed.
 
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