Cosmology curiosity Options

[dvandorn]

I've tried to ask this kind of question on one or two physics forums and have been soundly humiliated because I cannot arrive independently at the mathematical equations that define the inflation theory (i.e., "if you have to ask for explanations of the math in English, you are far too stupid to speak with us and should stop worrying your tiny little brain over matters that you, unlike us, can never hope to understand" -- that's darned near a direct quote). I'm kind of hoping one of our people here can point me to a source, or explain in English words, what is wrong with my issue, here.

It has to do with the fact that dark matter is apparently immune from being ingested into the supermassive black holes that occupy the centers of all the galaxies, as far as we can tell. A report in one of the popular science magazines from last year (IIRC) stated that this has been definitely proven -- that the derived distribution of dark matter and its derivedly-observed behavior when galaxies collide prove that dark matter is not attracted gravitationally to regular matter.

The article stated that this observation means we have to rethink all of our concepts of dark matter being composed of weakly interacting massive particles -- that any particle with mass must inevitably be attracted to other massive particles (and particularly to black holes), regardless of how weakly they interact.

I've seen nothing published since then. My basic curiosity is, how can dark matter affect regular matter gravitationally but not vice-versa? Anyone seen any theories about this, any publications you could point me towards? I find nothing in internet searches beyond this article I mentioned.

-the other Doug

[fredk]

Doug, I'm not sure what story you're referring to - could you post a link?

But definitely dark matter is attracted to ordinary matter (and v versa!) gravitationally. In fact, that's the only way we know about dark matter - it interacts so weakly with ordinary matter by all other means (electromagnetism, or light, etc), that no one has ever found evidence of such non-gravitational interactions. In other words, no one has ever seen dark matter, we've only seen its gravitational effect on ordinary matter. But there is now overwhelming evidence that dark matter is there.

So dark matter will be attracted to black holes, like ordinary matter. But it's actually harder to fall into a black hole than you might think. It's like going to Mars. It's easier (takes less fuel) to get to Mars orbit than it is to land on Mars. To land, you have to slow down a lot, using fuel or braking from the atmosphere. Dark matter interacts so weakly that it's hard for it to slow down in order to fall into a black hole. Ordinary matter rubs against itself and the friction slows it down so it can fall in more easily.

[Explorer1]

(Disclaimer: I'm not a cosmologist)
My understanding is that Doug simply means that dark matter has such dramatic effects on ordinary matter (giving galaxies their spiral arms, etc.), but the reverse is not the case. The truly gigantic structures (dark matter 'halos') surrounding the visible galaxies simply aren't affected by the relatively miniscule visible matter, simply through their great distance.

Some of the more exotic explanations for this involve dark matter being in a separate 'brane' (parallel universe in layman's terms), whereby its gravitational influence 'leaks' here, but nothing else. This sieve would be one-way, so black holes have no more effect on it that we or anything we can see does.

See : http://arxiv.org/abs/1102.0825
I do not endorse one theory over another, of course.

[Gerald]

Dark matter interacts so weakly that it's hard for it to slow down in order to fall into a black hole. Ordinary matter rubs against itself and the friction slows it down so it can fall in more easily.

If you are right with this, it would mean that we could derive interaction properties of dark matter with itself. A priori it's just evident, that there is low non-gravitational interaction with standard model particles (including bosons).
If dark matter doesn't form accretion disks around black holes, this would mean, that there is very low non-gravitational interaction between (still hypothetical, imho) dark matter particles (WIMPS, e.g. neutralinos). And we just have gravitational waves induced by accelerated dark matter, leading to a loss of kinetic energy, and an ultimate drop into the black hole.
Loss of energy by gravitational waves occurs in relevant amounts only very close to a black hole.

[dvandorn]

Thanks, guys! Some very good ideas to chew on.

I *think* the original article I found was a news item in Sky and Telescope's online service. When I have a little time over the holiday weekend, I'll find it and link it.

Again, thanks!

-the other Doug

[nprev]

<MOD HAT ON> Reminder to all participants in this discussion to review rule 1.9 prior to commenting. So far so good, but let's remember the boundaries here. <MOD HAT OFF>

[centsworth_II]

Perhaps this article explains the situation that dvandorn is asking about. But no doubt we run into trouble with rule 1.9 against arguing alternative science, as evidenced by the next to last sentence in the article.

"It’s fair to say that this idea, Modified Newtonian Dynamics or MOND, is not a mainstream one."

I understand the logic of rule 1.9. -- this is exactly the type of discussion that leads to interminable debate with no possible resolution.

[nprev]

And accordingly, we're done here. Topic closed.