Is dark matter distribution clumpy or homogenous?

  • Thread starter BernieM
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While pondering the concept of dark matter with my puny brain, I came to a question I was unable to answer which seems to have some significant implications:

Is Dark Matter affected by gravity and therefore clumped up with other matter in the universe? or is it unaffected by gravity and spread out homogenously throughout the universe?

It seems that either situation presents some further questions to be answered.

If Dark Matter is clumpy and clumps up in the same regions as normal matter, and our calculations of the gravitational effects of 'normal matter' were done without the influence of the knowledge of dark matter, then it seems that normal matter would have a much lesser gravitational effect than we have given it credit for and so would require even more dark matter to exist to create the gravitational effects we see.

If Dark Matter is NOT clumpy and is evenly distributed throughout the universe then normal matter would have to have a much stronger gravitational effect than we have given it credit for. In a scenario of our galaxy, the gravitational effect of dark matter would be helping to keep all the stars in the galaxy from flying off into intergalactic space, where the dark matter in the vicinity of the galaxy beyond the galactic edge would be attempting to pull those stars away from the galactic center with a greater net force than the dark matter within the galaxy was pulling them in.
 

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  • #2
Janus
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The answer is that it clumps, but not as easily or to the same degree as "normal" matter. Normal matter has the advantage that it can interact in ways other than by gravity that aid its tendency to clump up.. It can adhere to itself and radiate away excess energy for instance.

DM does neither and has clumped much less. It has formed halos that effect gravity on the scale of galaxies, but there is an insignificant amount in our own Solar system.
 
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So then are you saying that in our galaxy that the dark matter is distributed like a donut, the center of the galaxy centered in the donut hole? If I visualize that correctly and dark matter accounts for 80% of the mass and gravity of the galaxy then why wouldn't the rest of the mass distribute itself in the same region as the dark matter?
 
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Conversion of dark matter into ultra-high-energy particles
Near an active galactic nucleus, one of these particles can fall into the black hole, while the other escapes, as described by the Penrose process. Some of the particles that escape will collide with incoming particles creating collisions of very high energy. It is in these collisions, according to Pavlov, that ordinary visible protons can form. These protons would have very high energies. Pavlov claims that evidence of this is present in the form of ultra-high-energy cosmic rays.
http://en.wikipedia.org/wiki/Ultra-high-energy_cosmic_ray
 
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Janus
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So then are you saying that in our galaxy that the dark matter is distributed like a donut, the center of the galaxy centered in the donut hole? If I visualize that correctly and dark matter accounts for 80% of the mass and gravity of the galaxy then why wouldn't the rest of the mass distribute itself in the same region as the dark matter?
No, you are thinking about a different type of "halo" which is the optical effect that is seen as a ring of light.

The dark matter halo is a roughly spherical cloud in which the visible galaxy is imbedded.
 

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