What are the mysterious properties of Dark Matter?

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Discussion Overview

The discussion revolves around the properties of dark matter and its relationship with dark energy, exploring theoretical implications, observational evidence, and the nature of these phenomena in astrophysics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants express uncertainty about the properties of dark matter, noting that while it exerts gravitational pull, its exact nature remains unknown.
  • One participant questions whether dark matter could affect the redshift of light from distant galaxies, suggesting a lack of understanding about its properties.
  • Another participant asserts that dark matter does not interact with electromagnetic radiation or baryonic matter, which is a key characteristic that distinguishes it from other forms of matter.
  • There is a discussion about the historical context of dark energy and dark matter, with references to Einstein's cosmological constant and its implications for the universe's expansion.
  • Some participants propose a potential connection between dark matter and dark energy, suggesting that they might be related phenomena, while others argue that they are fundamentally different.
  • Concerns are raised about the terminology used to describe dark matter and dark energy, with suggestions for alternative names that might reduce confusion.
  • Participants discuss the observational evidence for dark matter, including its gravitational effects, and question how we can be certain it does not interact with light or baryonic matter.
  • There is a debate over the possibility that a portion of dark matter could be baryonic matter, specifically MACHOs, which are not directly observable.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the properties and implications of dark matter and dark energy. While some points are clarified, there remains significant uncertainty and competing views about their relationship and characteristics.

Contextual Notes

Participants highlight limitations in current understanding, including the definitions of dark matter and dark energy, and the unresolved nature of their interactions with light and baryonic matter.

  • #31
paisiello2 said:
This dark matter is sure strange stuff.

Yep. Hopefully future observations will shed some light on the subject. Pun very, very intended.
 
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  • #32
Drakkith said:
Yep. Hopefully future observations will shed some light on the subject. Pun very, very intended.

It is a shame that it is difficult to study dark matter. It is not like we can just go out there and get a sample of it to study in a lab. However, mysteries like this is what keeps me interested and amazed by astrophysics. I hope to be alive when they shed some light on the dark.

cb
 
  • #33
Drakkith said:
Yep. Hopefully future observations will shed some light on the subject. Pun very, very intended.

You are evil.
 
  • #34
Drakkith said:
Well, not only can we not see it, but the way dark matter seems to interact makes us believe that it doesn't interact with the EM force. For example, most of the dark matter in our galaxy seems to be on the outside in a large, spherical shell. This makes perfect sense if dark matter doesn't interact through the EM force, since infalling dark matter (matter that falls out of the shell and into the galaxy) doesn't seem to be able to lose this energy and clump together. If it could, then we wouldn't have a halo of dark matter, as it would have clumped together long ago just like normal matter did. Instead, it simply passes through the galaxy without interacting with anything and goes right out the other side where it gradually slows down under gravity, spending most of its time in the halo.
And yet in other cases, such as Abell 520, it seems that dark matter DOES clump. This is a big puzzle.
http://www.space.com/14773-strange-dark-matter-colliding-galaxies.html
 
  • #35
Bill_K said:
And yet in other cases, such as Abell 520, it seems that dark matter DOES clump. This is a big puzzle.
http://www.space.com/14773-strange-dark-matter-colliding-galaxies.html

Interesting. I hadn't read this before. It wonder if the dark matter is actually clumping or if it's just something like an artifact, possibly due to a filament of dark matter aligned with us. (A possible explanation I found on wiki's page on abell 520) Either way, exciting times!
 
  • #36
Published maps show dark matter as clumps and threads throughout the visible universe as modeled through gravitational lensing. I understand the concept that it does not interact with visible matter or light except through gravity. Even if we see no interaction by strong, weak or electromagnetic forces wouldn't it interact with itself gravitationally? How do clumps not grow denser to the point of aggregation? Why do we not see dark matter dark holes?
 
  • #37
pjkarn6 said:
Published maps show dark matter as clumps and threads throughout the visible universe as modeled through gravitational lensing. I understand the concept that it does not interact with visible matter or light except through gravity. Even if we see no interaction by strong, weak or electromagnetic forces wouldn't it interact with itself gravitationally? How do clumps not grow denser to the point of aggregation? Why do we not see dark matter dark holes?

As an example, let's consider two hypothetical dark matter particles in empty space. The two particles will fall towards each other under the force of gravity, gaining kinetic energy as they accelerate. However, since they do not act via the EM force, they have no way of losing this kinetic energy except through gravity. So the two particles pass right through each other (since there is no force to stop them like there is with regular particles) and begin to slowly decelerate under gravity as they recede from one another. The two DM particles eventually wind up just as far apart as they initially were before they begin to fall back towards each other to repeat the process. In order to clump together DM must lose the kinetic energy it gains when it falls towards other objects. There simply isn't a good way for it to do this though.
 
  • #38
just to add to Drakkkith's excellent answer DM also does not show any strong force interaction. So there is no strong force to hold two dark matter particles together if the two particles were close enough for the strong force to act upon them
 
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