What are the mysterious properties of Dark Matter?

[Drakkith]

This dark matter is sure strange stuff.

Yep. Hopefully future observations will shed some light on the subject. Pun very, very intended.

 

[Cosmobrain]

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

 

[phinds]

Yep. Hopefully future observations will shed some light on the subject. Pun very, very intended.

You are evil.

 

[Bill_K]

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

 

[Drakkith]

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!

 

[pjkarn6]

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?

 

[Drakkith]

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.

 

[Mordred]

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