Can Anybody Tell The Latest on Dark Matter?

[BigDon]

Good morning everybody,

I'd offer coffee but...

I noticed in some other threads that some ideas concerning non-baryonic dark matter have been reconsidered. Some things like how it's mass effects the rotation rate of the stars in galaxies. And how much mass of the Universe it is supposed to comprise. Stuff like that.

Plus a brief "state of the union" on the best explaination so far would be nice too. I read links, so that's cool too. I just trust you guys to be the "woo filter" better than google. Somehow typing in "Dark Matter, No **" doesn't seem to sound helpful.

This non-baryonic dark matter is much weirder to me than black holes.

Thank you.

[John Mendenhall]

Last thing I saw was the folks speculating on local dark matter in the solar system. Yes, it was serious work. The idea essentially was: if there is dark matter, and if it interacts only gravitaionally, then the solar system should pick up some tag along DM. And loose some, too. The question was, how much, and where is the equilibrium point (similar to chemical equilibriums, I think).

The work was aimed at detection possibilities. As I recall, it was covered in a story on the home page here.

[Tim Thompson]

I noticed in some other threads that some ideas concerning non-baryonic dark matter have been reconsidered.

I don't follow enough threads to know who's talking about what. But I don't think it matters much anyway. Since nobody knows what dark matter is, re-thinking things that we can barely think in the first place hardly feels like significant news.

This non-baryonic dark matter is much weirder to me than black holes.

It shouldn't. Neutrinos, for instance, are in fact non-baryonic dark matter. So all we are talking about really is just more of basically the same kind of stuff we already know about. That does not seem particularly weird to me.

Last thing I saw was the folks speculating on local dark matter in the solar system.

See, i.e., Xu & Seigel, 2008; Frère, Ling & Vertongen, 2008; Ganguly, et al., 2007; Sereno & Jetzer, 2006. But I think all of this is a think more than a rethink.

[trinitree88]

Big Don. One of the things that occurred was that they detected oxygen with ultraviolet telescopy that was not hot enough to emit x-rays, but was visible in the ultraviolet. There was enough of it around the halos of galaxies that the need for dark matter was reduced about 50%. ...and they're just starting to look this way. pete


see:http://www.physorg.com/news130516845.html

[byronm]

Big Don. One of the things that occurred was that they detected oxygen with ultraviolet telescopy that was not hot enough to emit x-rays, but was visible in the ultraviolet. There was enough of it around the halos of galaxies that the need for dark matter was reduced about 50%. ...and they're just starting to look this way. pete


see:http://www.physorg.com/news130516845.html

I'll have to check that out.. i found some other papers that theorized redshift by molecular hydrogen and that there is more molecular hydrogen than originally suspected and that was a piece of the missing mass puzzle as well.

[parejkoj]

Big Don. One of the things that occurred was that they detected oxygen with ultraviolet telescopy that was not hot enough to emit x-rays, but was visible in the ultraviolet. There was enough of it around the halos of galaxies that the need for dark matter was reduced about 50%. ...and they're just starting to look this way. pete

see:http://www.physorg.com/news130516845.html

Ah, no. The need for dark matter is still there. These observations don't change that at all. The "missing matter" in this case was ordinary baryonic matter that should have been there, based on elemental abundances predicted by the big bang + subsequent nucleosynthesis, but wasn't seen until these observations.

[trinitree88]

Ah, no. The need for dark matter is still there. These observations don't change that at all. The "missing matter" in this case was ordinary baryonic matter that should have been there, based on elemental abundances predicted by the big bang + subsequent nucleosynthesis, but wasn't seen until these observations.

parejkoj. "
The presence of highly ionized oxygen (and other elements) between the galaxies is believed to trace large quantities of invisible, hot, ionized hydrogen in the universe. These vast reservoirs of hydrogen have largely escaped detection because they are too hot to be seen in visible light, yet too cool to be seen in X-rays. "

link's words above. Since the quintionized oxygen traces out the hydrogen that is otherwise invisible, what mechanism is proposed to say that the same vast reservoirs of hot hydrogen cannot exist on the periphery of galaxies? It would seem to be that the lighter elements, mixed in with a soup of heavier ones, would have a higher RMS velocity and diffuse more rapidly out of a fireball, leaving galaxies in general with halos of hot hydrogen...Graham's Law, No?
pete

see:http://chandra.harvard.edu/photo/2000/0015multi/

and see:http://sci.esa.int/science-e/www/obj...objectid=12820

[BigDon]

Thank you everybody.

[John Mendenhall]

Various posters, thanks for the links.

If DM turns out to be baryonic and mostly hydrogen, it certainly takes care of the problem.

[byronm]

Ah, no. The need for dark matter is still there. These observations don't change that at all. The "missing matter" in this case was ordinary baryonic matter that should have been there, based on elemental abundances predicted by the big bang + subsequent nucleosynthesis, but wasn't seen until these observations.

This doesn't compute

Isn't the foundation of dark matter/dark energy simply matter/energy that "should be there" but we couldn't see/explain? If we find missing matter isn't that a point for gravity and one less point for that dark stuff?

[01101001]

If we find missing matter isn't that a point for gravity and one less point for that dark stuff?

How does the scoring work?

Wasn't dark matter always considered subject to gravity and first described as a source for gravitational effects?

(Or, are you thinking not of dark matter, but of dark energy?)

[byronm]

How does the scoring work?

Wasn't dark matter always considered subject to gravity and first described as a source for gravitational effects?

(Or, are you thinking not of dark matter, but of dark energy?)

Of course dark matter was always considered subject to gravity.. dark matter was invented because some form of matter "HAD" to be there and we simply couldn't see it. (for simplicity sake)

The same "HAD" to be there translates to dark energy. For the universe to be expanding there HAS to be dark energy. I guess my kudos to gravity is that finding of real "matter" is a point for gravity and that as we add to the known "matter" out there we will negate the need for "Dark matter" and on the flip side of that we may negate the need for "Dark energy" since we may be able to prove or theorize things with more knowns of the whys & ifs.

dark matter/dark energy are really bad names. Dark matter seems to describe missing mass that has a gravitational effect but dark energy is something that is somewhat anti-gravity and used to explain the expansion of the universe. Thus personally i'm thrilled when gravity as we understand it with items that have mass as we understand it comes out in the end.

[Cougar]

This doesn't compute ... Isn't the foundation of dark matter/dark energy simply matter/energy that "should be there" but we couldn't see/explain?

No, it's not that simple. As briefly explained in Wiki....

...all of the light element abundances depend on the amount of ordinary matter (baryons) relative to radiation (photons).

So, if I understand it correctly, the observed proportions of the primordial elements indicate how many baryons there should be. Apparently we didn't see that many. Now what we see is closer to what is expected.

For a classic exposition on this and other topics, check out The First Three Minutes by Weinberg.

[loglo]

This doesn't compute

Isn't the foundation of dark matter/dark energy simply matter/energy that "should be there" but we couldn't see/explain? If we find missing matter isn't that a point for gravity and one less point for that dark stuff?

Yes it does. Out of the "visible in principle" baryonic matter only some of it is actually visible to us. The rest is too far away or obscured or whatever. This paper was just describing finding some of the previous type of material which hadn't been observed but as parejkoj says was expected to be there. It does not change the amount of non-baryonic "not visible even in principle " matter in the universe required to explain the observations.

I agree though that they are really bad names - if just for the fact they have chronically confused the general public.

[trinitree88]

Yes it does. Out of the "visible in principle" baryonic matter only some of it is actually visible to us. The rest is too far away or obscured or whatever. This paper was just describing finding some of the previous type of material which hadn't been observed but as parejkoj says was expected to be there. It does not change the amount of non-baryonic "not visible even in principle " matter in the universe required to explain the observations.

I agree though that they are really bad names - if just for the fact they have chronically confused the general public.

Which leaves us with the need to isolate the mechanism whereby the missing hydrogen/ baryonic matter will be able to form "threads" between the galaxy clusters, having been ejected from galaxies at escape velocity, without leaving an equally invisible halo of sub-escape-velocity mix of gases. I am particularly interested to see how hydrogen, being the lightest gas in the primordial mix of elements will not end up with the highest RMS velocity,and as such the outer periphery of the galactic halo.. as stipulated by Graham's Law. Even subtle differences in mean molar masses enable isotopic separation processes to take place...witness the UF₆ separation of Oak Ridge using terra cotta plates. pete

[parejkoj]

Who said this Hydrogen was ejected from galaxies? It was there from the beginning, the Oxygen was dumped on it from galaxies, not the other way around. Read the press release again: they do a decent job describing it.

[byronm]

Yes it does. Out of the "visible in principle" baryonic matter only some of it is actually visible to us. The rest is too far away or obscured or whatever. This paper was just describing finding some of the previous type of material which hadn't been observed but as parejkoj says was expected to be there. It does not change the amount of non-baryonic "not visible even in principle " matter in the universe required to explain the observations.

This doesn't compute either.

The matter is expected period. It doesn't matter (hehe) what it was but the fact we can isolate it to baryonic matter seems to convey to me that we're discovering what we perceived as dark matter and filling in the "Expected" matter regardless.

[parejkoj]

This older BAUT thread is still relevant here, and many of the responses to this later thread are also good. These should do a good job answering the question posed in the OP.

Byronm: your confusion should be answered in those threads.

Heck, the Wikipedia article on DM is actually pretty good, and could help direct you to other reading.

[loglo]

Which leaves us with the need to isolate the mechanism whereby the missing hydrogen/ baryonic matter will be able to form "threads" between the galaxy clusters, having been ejected from galaxies at escape velocity, without leaving an equally invisible halo of sub-escape-velocity mix of gases. I am particularly interested to see how hydrogen, being the lightest gas in the primordial mix of elements will not end up with the highest RMS velocity,and as such the outer periphery of the galactic halo.. as stipulated by Graham's Law. Even subtle differences in mean molar masses enable isotopic separation processes to take place...witness the UF₆ separation of Oak Ridge using terra cotta plates. pete

Interesting. Locally, most of the observed neutral gas in our galactic halo is in the form of low metallicity High Velocity Clouds which are thought to be either infalling remnants of galaxy formation or stripped from the Magellanic Clouds via tidal interaction. Only a small portion have a "galactic fountain" origin ie supernova-ejected gas with near-solar metallicity, and they are restricted to about 10kpc from the disc. see eg Richter et al 2001.

Since the HVC's consist of molecular hydrogen which generally only forms in intergalactic space in the presence of dust grains of metals I'm wondering if the dust grains are the major contributor to metallicity in the halo and whether that would basically make levels of any isotopic separation unobservable?

[byronm]

This older BAUT thread is still relevant here, and many of the responses to this later thread are also good. These should do a good job answering the question posed in the OP.

Byronm: your confusion should be answered in those threads.

Heck, the Wikipedia article on DM is actually pretty good, and could help direct you to other reading.

I started from the wiki article and this statement is which brought me here:

"Some hard-to-detect baryonic matter makes a contribution to dark matter but constitutes only a small portion.[3][4] Determining the nature of this missing mass is one of the most important problems in modern cosmology and particle physics."

Is that actually false?

[loglo]

No its not. "Dark matter" consists of baryonic and non-baryonic dark matter.

Baryonic matter makes up 4% of the universe, but only a fraction is visible in the form of stars, dust etc. That is the stuff being talked about in the article.

Non-baryonic dark matter makes up 24% of the universe and is, even in principle, undetectable by conventional means. It just doesn't interact with photons.

Just because they find a little bit more of the first type doesn't mean you can subtract it from the 2nd type. There is still plenty of undetected normal matter to be discovered.

[byronm]

No its not. "Dark matter" consists of baryonic and non-baryonic dark matter.

Baryonic matter makes up 4% of the universe, but only a fraction is visible in the form of stars, dust etc. That is the stuff being talked about in the article.

Non-baryonic dark matter makes up 24% of the universe and is, even in principle, undetectable by conventional means. It just doesn't interact with photons.

Just because they find a little bit more of the first type doesn't mean you can subtract it from the 2nd type. There is still plenty of undetected normal matter to be discovered.

At what point though do you sit back and say "hey, there may be a lot more normal matter than we give credit" and start subtracting from the overall requirement of dark matter (and any types thereof)?

On an unrelated note, what is the political ramifications of understanding and defining dark matter if it indeed does exist? Would normal people even find out about it? Wouldn't understanding dark matter lead to harnessing dark matter? deep thoughts

[parejkoj]

At this point, we have a pretty good idea about where most of the ordinary matter should be. Studies like the one in the press release that trinitree88 first posted are done to find this "dark" baryonic matter. The list of observational evidence for dark matter in the first BAUT thread I linked to includes things where baryonic matter just won't work, e.g. baryon acoustic oscillations, CMB acoustic peaks and the bullet cluster.

[John Mendenhall]

At this point, we have a pretty good idea about where most of the ordinary matter should be.

So they're talking about the limited case of undetected baryonic matter, not the more general case of DM? We still get the 4% baryonic and 24% something else?

[parejkoj]

So they're talking about the limited case of undetected baryonic matter, not the more general case of DM? We still get the 4% baryonic and 24% something else?

Yes and yes. There are multiple lines of evidence for the fraction of baryonic matter, many of which are described in the BAUT links I gave. Some of those methods are dependent on dark matter being dark (not interacting electromagnetically, and thus not cooling via friction, etc.), and so are independent of observations like this that find "light matter."

[John Mendenhall]

Yes and yes. There are multiple lines of evidence for the fraction of baryonic matter, many of which are described in the BAUT links I gave. Some of those methods are dependent on dark matter being dark (not interacting electromagnetically, and thus not cooling via friction, etc.), and so are independent of observations like this that find "light matter."

Rats. Well, back to the undetectable particle detector.

Thenks, John M.