PDA

View Full Version : is a galaxy's DM halo in motion



nota
2011-Oct-25, 04:35 AM
is a galaxy's DM halo in motion
is that motion in orbit around the galaxy's center in mass
or as each star is in it own orbit
is each bit of DM on an independent orbit from all others
so random or coherent motion

like a cloud of gas & dust has an orbit
and each bit of matter may move in the cloud
but few will leave the cloud or go join an other cloud

the gravity with out clumping gets me
gravity is mass curved space
curved space should cause mass clumps
how is DM's anti-clumping force purposed to work
some how anti-clumping looks to be strange
and almost like anti-gravity at short range

antoniseb
2011-Oct-25, 05:15 AM
... how is DM's anti-clumping force purposed to work...

DM doesn't have anti-clumping force any more than vacuum has sucking power.
Your earlier notes about each DM particle being on an independent (frequently perturbed) orbit is right. Each one is moving rapidly compared to the stars and ISM that we see, so they don't stick around and clump in our position. They just keep cruising and the perturbations of the things they pass or whiz through average out (mostly).

TooMany
2011-Nov-04, 11:13 PM
Isn't the question quite difficult to answer, since DM particles do not interact except through gravity? Maybe they have angular momentum and the DM halos spin? Who knows?

It's fun to talk about them like they actually exist. You can assign (within some bounds) whatever properties you like, since nobody has detected them let alone measured any properties. DM is more about what we don't know than about anything we actually know. It's probably the most urgent issue to be resolved in cosmology at this time.

Strange
2011-Nov-04, 11:15 PM
You can assign (within some bounds) whatever properties you like,

Those bounds are fairly tightly constrained.


It's probably the most urgent issue to be resolved in cosmology at this time.

Interesting, maybe. But urgent?

Cougar
2011-Nov-04, 11:54 PM
is a galaxy's DM halo in motion

Yes.


is that motion in orbit around the galaxy's center in mass

Yes.


is each bit of DM on an independent orbit from all others

Yes.


like a cloud of gas & dust has an orbit
and each bit of matter may move in the cloud

Only very vaguely, but this analogy quickly fails for DM. Gas and dust interact in the same way your computer monitor interacts with your desk. It doesn't fall through because the electrons in the desk atoms repel the electrons in the base of the monitor. DM doesn't do this. How do we know? Because if it did, there would be tell-tale signs. We see no such signs.


the gravity with out clumping gets me
gravity is mass curved space
curved space should cause mass clumps

Only if the mass runs into other mass and interacts. DM apparently sails right through mass and even other DM particles without interacting, or only very rarely.


how is DM's anti-clumping force purposed to work

By not interacting with regular matter, or even other DM.


some how anti-clumping looks to be strange

Oh, it is. But it's not unheard of. Neutrinos rarely interact with anything, and then only via the weak nuclear 'force."

cjameshuff
2011-Nov-05, 04:08 AM
As a couple people have mentioned, there is no anti-clumping force, just a lack of the energy-absorbing and energy-shedding phenomena that allow normal matter to clump. Colliding atoms put some kinetic energy into knocking electrons off or bumping them into different energy levels, and molecules trap energy in vibrational modes. Kinetic energy gets converted to (and escapes as) thermal radiation, allowing the normal matter to cool and form dense clumps, aided further by matter's tendency to form chemical bonds and form heavier molecules, and for the heavier elements, much larger solid particles.

Dark matter doesn't interact electromagnetically, it can't radiate excess energy, and can basically only cool by its gravitational interactions with normal matter, so it forms diffuse halos instead of clumping.

chornedsnorkack
2011-Nov-05, 09:04 AM
Do dark matter haloes rotate?

Are the dark matter haloes precisely centrally symmetric? Or do they possess deviations from central symmetry exactly what is caused by the gravitational influence of non-centrally-symmetric light matter within? Or do they possess flattening caused by rotation of dark matter halo itsely?

antoniseb
2011-Nov-05, 10:58 AM
Do dark matter haloes rotate?

Are the dark matter haloes precisely centrally symmetric? Or do they possess deviations from central symmetry exactly what is caused by the gravitational influence of non-centrally-symmetric light matter within? Or do they possess flattening caused by rotation of dark matter halo itsely?

Take a look at the bullet cluster images that show the location of dark matter via weak lensing studies. The answer is that after a long time, any dark matter halo will tend toward looking spherically symmetric in the large, but they can be disturbed by gravity from other objects (or in mergers) in the short term.

chornedsnorkack
2011-Nov-05, 12:51 PM
The answer is that after a long time, any dark matter halo will tend toward looking spherically symmetric in the large, but they can be disturbed by gravity from other objects (or in mergers) in the short term.

Does dark matter conserve angular momentum, or does it not?

antoniseb
2011-Nov-05, 01:18 PM
Does dark matter conserve angular momentum, or does it not?
In every mainstream model for what Dark Matter is, yes, it conserves angular momentum... but it is not easy for it to transfer angular momentum: only by gravity.

chornedsnorkack
2011-Nov-05, 01:29 PM
In every mainstream model for what Dark Matter is, yes, it conserves angular momentum... but it is not easy for it to transfer angular momentum: only by gravity.

If, in mergers, dark matter acquires net angular momentum, should it then settle into a spherically symmetric distribution, or an axially symmetric distribution which is significantly nonspherical?

antoniseb
2011-Nov-05, 01:41 PM
If, in mergers, dark matter acquires net angular momentum, should it then settle into a spherically symmetric distribution, or an axially symmetric distribution which is significantly nonspherical?
It should be ellipsoidal. There may be a settling time that brings it back to spherical, but there could also be an influence from the 20% of the mass of the whole which is baryonic matter. I am very hesitant to say it will always be a perfect sphere.

trinitree88
2011-Nov-05, 04:47 PM
Since the implementation of the paradigm of dark matter we have seen many new things.
1. Until dark matter appeared, it appeared that a detector in a particle physics lab could find an intact hierarchy of conservation laws, with energy/mass being conserved and momentum, both linear and angular always conserved.
2. Should dark matter not conserve angular or linear momentum, that would be a first in the long and storied history of physics.....through trillions of observations.
3. In addition, it was seen historically that the weak interaction acts via the weak force(no quotation marks needed here for force).... in the Standard Model of Particle Physics, via the three vector bosons, the W(sup)+(/sup),W(sup)-(/sup), and Z(sup)0(/sup)...universally. That means it acts on everything, the way gravity does. Now the dark matter supercedes that and does not act with neutrinos via any of them. That also is new. That means that dark matter is not only invisible to your eyes electromagnetically, it is also invisible to particle detectors weakly.
4. I'll bet a hot fudge sundae that when the JWST is launched, the new data with the higher resolution spectrographs will make dark matter history. pete

TooMany
2011-Nov-05, 05:08 PM
Those bounds are fairly tightly constrained.

Yes and no. Dwarf galaxy studies are compounding the "cuspy halo problem", so now we start to get proposals for "warm dark matter' or somewhat self-interacting dark matter and so on. So perhaps there is some room to tweak DM assumptions.


Interesting, maybe. But urgent?

Well, we have a theory of gravitation that has been very successful locally (GR) however we seem unable to explain the rotation of galaxies in the local group, including our own so we have hypothesized that an invisible unknown form of matter constitutes 80% of matter in galaxies. That's a big problem. Our measurements of rotational curves in nearby galaxies are quite reliable. No detection of the new invisible form of matter has occurred even though the rotation problem was clear in the 1970's. It seems to me a fundamental problem because it's so well established, unlike speculations about the state of the universe at z > 4.

Why do we favor this non-baryonic explanation? Is it because the big bang theory nucleosynthesis arguments need this non-baryonic matter to achieve consistency with observations?

But perhaps that's where our mistake lies - in insisting that it must be non-baryonic. Here are a number of papers which argue that the rotation curves are explained by the existing theory of gravity and undetected dark baryonic matter in the less luminous to non-luminous extensions of the thin galactic disks.

http://arxiv.org/abs/0803.0556v1
http://arxiv.org/abs/0804.3203v1
http://arxiv.org/abs/0804.0217v1
http://arxiv.org/abs/astro-ph/0309823v1
http://arxiv.org/abs/0810.0314v1
http://arxiv.org/abs/0903.1962v1
http://arxiv.org/abs/0806.1131v4
http://arxiv.org/abs/astro-ph/0703430v7
http://arxiv.org/abs/astro-ph/9402026v1

Here's an interesting photo of overlapping spirals that lends some direct support to the possibility that large amounts of baryonic dark matter surround the visible disks of spiral galaxies:

http://imgsrc.hubblesite.org/hu/db/images/hs-2008-33-a-large_web.jpg

Here's a paper that discusses this:

http://arxiv.org/abs/0810.2646v1

Bear in mind also that what you see in the photo is cold dust. It is quite possible that very cold molecular clouds also populate the outer reaches of galaxies, but these may be transparent depending on the dust content, and undetectable by emissions.

So why are we chasing after mysterious non-baryonic dark matter to explain galactic rotation curves?

korjik
2011-Nov-05, 05:11 PM
Since the implementation of the paradigm of dark matter we have seen many new things.
1. Until dark matter appeared, it appeared that a detector in a particle physics lab could find an intact hierarchy of conservation laws, with energy/mass being conserved and momentum, both linear and angular always conserved.

Actually, GR has made conservation laws local since 1919, and particle accelerators are local, so they still see all the conservation laws.


2. Should dark matter not conserve angular or linear momentum, that would be a first in the long and storied history of physics.....through trillions of observations.

Is there someone who dosent think that dark matter obeys conservation laws?


3. In addition, it was seen historically that the weak interaction acts via the weak force(no quotation marks needed here for force).... in the Standard Model of Particle Physics, via the three vector bosons, the W(sup)+(/sup),W(sup)-(/sup), and Z(sup)0(/sup)...universally. That means it acts on everything, the way gravity does. Now the dark matter supercedes that and does not act with neutrinos via any of them. That also is new. That means that dark matter is not only invisible to your eyes electromagnetically, it is also invisible to particle detectors weakly.

And? Certain types of particles not interacting with certain types of forces is not new. Electrons dont do the strong force, neutrinos dont do electromagnetism. The fact DM only interacts gravitationally isnt all that an unusual thing.


4. I'll bet a hot fudge sundae that when the JWST is launched, the new data with the higher resolution spectrographs will make dark matter history. pete

Why? What is JWST supposed to see? Alot of the parameter space for small visible objects is already excluded from ground based observations.

Shaula
2011-Nov-05, 06:02 PM
So why are we chasing after mysterious non-baryonic dark matter to explain galactic rotation curves?
Because in general the models using it fit the evidence better.

TooMany
2011-Nov-05, 08:48 PM
Because in general the models using it fit the evidence better.

BB evidence you mean? Looking to nuclear formation calculations to explain rotation curves is rather round about. It's like saying, even if we can explain galaxy rotation curves with our existing theories and the assumption of an extended normal matter halo in the galactic planes, we should reject such an explanation but it doesn't help explain the BBT nuclear abundances. That does not make sense to me at all.

To make the simple explanation work, we need evidence of the additional baryonic matter. I showed you some direct evidence. Do you care to comment on that?

The missing mass estimates are based on the assumption that the distribution of all normal matter in galaxies is the same as the distribution of luminous matter (mostly stars). That seems like a very poor assumption. Just type "edge-on galaxies" into google images and look at the band of dark matter that is dense enough to block most of the light from the edge to center of each galaxy.

Do you suppose that the Plank mission will be sensitive enough to see cold matter around the Andromeda galaxy that we have been unable to see in the past?

Cougar
2011-Nov-05, 09:50 PM
....the rotation problem was clear in the 1970's.

Actually, Zwicky noticed it in 1933.


So perhaps there is some room to tweak DM assumptions.

There's always room for that. It's usually called finding new evidence.


That's a big problem.

Of course it is. And of course there have been ambitious surveys using clever methods seeking to detect every reasonable possibility that could explain this. They've only found minor additions to the baryonic mix. But to put this in perspective, if Galileo's 1610 report on the moons of Jupiter can be considered the beginning of astronomical telescopic observation, it took well over 300 years to settle the question of whether the Milky Way was the entire Universe or not!

TooMany
2011-Nov-05, 10:23 PM
Actually, Zwicky noticed it in 1933.

Zwicky drew conclusions from the Coma Cluster in 1933, not galaxy rotation curves.


Of course it is. And of course there have been ambitious surveys using clever methods seeking to detect every reasonable possibility that could explain this. They've only found minor additions to the baryonic mix. But to put this in perspective, if Galileo's 1610 report on the moons of Jupiter can be considered the beginning of astronomical telescopic observation, it took well over 300 years to settle the question of whether the Milky Way was the entire Universe or not!

I'm not that patient. :o But you make a good point. Things that are hard to detect are just that, until the right instrumentation comes along and finally settles the issue.

Imagine an alien on the moon observing a campfire on the earth at night. With his spectroscope he might detect nitrogen, oxygen, and so on in the flames. Beyond the flames he would detect nothing, but he would be foolish to assume those chemicals only exist in the flames.

Shaula
2011-Nov-05, 10:49 PM
BB evidence you mean? Looking to nuclear formation calculations to explain rotation curves is rather round about. It's like saying, even if we can explain galaxy rotation curves with our existing theories and the assumption of an extended normal matter halo in the galactic planes, we should reject such an explanation but it doesn't help explain the BBT nuclear abundances. That does not make sense to me at all.
You are looking at one thing, in isolation. My point was that it is irrelevant if your baryonic matter fits one bit of evidence as well as the CDM model. What matters is how it fits into the big picture too. It doesn't matter if you find a hoof print in your bedroom if the door is too small for a horse.

We've had this argument before. Not going to comment, not going to get sucked in. You want to argue this go to the ATM section and write a full description of the ideas you feel confident enough to defend.

Tensor
2011-Nov-05, 10:49 PM
But perhaps that's where our mistake lies - in insisting that it must be non-baryonic. Here are a number of papers which argue that the rotation curves are explained by the existing theory of gravity and undetected dark baryonic matter in the less luminous to non-luminous extensions of the thin galactic disks.

http://arxiv.org/abs/0803.0556v1
http://arxiv.org/abs/0804.3203v1
http://arxiv.org/abs/0804.0217v1
http://arxiv.org/abs/astro-ph/0309823v1
http://arxiv.org/abs/0810.0314v1
http://arxiv.org/abs/0903.1962v1
http://arxiv.org/abs/0806.1131v4
http://arxiv.org/abs/astro-ph/0703430v7
http://arxiv.org/abs/astro-ph/9402026v1

This is hilarious. You want to show how all these are compatible? I'll save you the trouble, they're not. None of these support the others, except perhaps for the first three, which are self referential(which is a big red flag), and two others, who have the same author. So, you have again, resorted to the shotgun approach, hoping something will stick. Exactly ONE of those has gone through peer review. Which pretty much puts all the above into the fringe category.


Here's an interesting photo of overlapping spirals that lends some direct support to the possibility that large amounts of baryonic dark matter surround the visible disks of spiral galaxies:

http://imgsrc.hubblesite.org/hu/db/images/hs-2008-33-a-large_web.jpg

Here's a paper that discusses this:

http://arxiv.org/abs/0810.2646v1

Yeah, did you miss the part about the foreground galaxy being unusual, because of the extent of the dust? The " We explore the radial and spatial distribution and the inferred extinction law of the dust in a smaller foreground spiral, which displays an extent of dust hitherto unseen in backlit galaxies." Which means previous galaxies that were backlit, didn't have as much dust as this one. Meaning observations don't support lots of dust outside the optical disk and backlit HI would be seen if there was a lot of it. Some of it has been seen, in backlit galaxies, but not the amount you seem to think there is.


Bear in mind also that what you see in the photo is cold dust.

It is quite possible that very cold molecular clouds also populate the outer reaches of galaxies,

Contrary to what you seem to think, this has been taken into account. From the paper:"The interstellar matter (ISM) extends to large radii in the form of atomic hydrogen (HI) but thus far there is little direct evidence of dust beyond the optical disk..."


but these may be transparent depending on the dust content, and undetectable by emissions.

Yeah, but, again from the paper: "In contrast, backlit dust can be detected independent of its temperature."


So why are we chasing after mysterious non-baryonic dark matter to explain galactic rotation curves?

Because there just isn't enough baryonic mass observed. Oh, by the way, this paper.... can't be used, if you using any of the other ones above as this one is incompatible with the ones above. So which one is it? You need to pick what you think is the problem and stick with it. Just because someone may not understand or doesn't like what current thought is, and writes a paper on it, doesn't mean there is actually anything to it.

TooMany
2011-Nov-06, 12:33 AM
This is hilarious. You want to show how all these are compatible? I'll save you the trouble, they're not. None of these support the others, except perhaps for the first three, which are self referential(which is a big red flag), and two others, who have the same author. So, you have again, resorted to the shotgun approach, hoping something will stick. Exactly ONE of those has gone through peer review. Which pretty much puts all the above into the fringe category.

You are a very quick study. Of course some of them are self referential, the same authors wrote a number of papers bringing in more detailed considerations. Which one is peer-reviewed? Cooperstone's is I'm pretty sure because he claims to have responded to all criticism and has not heard any more. What they have in common however is a attempt to model spiral galaxies without reference to non-baryonic matter. Most address the issue of in-disk distribution of normal dark matter outside the luminous part. It appears that there isn't much interest in this mundane explanation in the "mainstream".

A lot of analysis is required to figure out just how much dark matter and in what configurations can explain the rotational curves. Unfortunately it appears the majority of papers start with the assumption that the DM is distributed spherically (because of the claimed properties of the non-baryonic matter) and then conclude from that how much is required.

It's rather difficult to find papers that assume that dark stuff that we cannot see is just plain old matter and derive sensible distributions to account for rotation curves. To examine all possibilities, surely this possibility should be carefully studied and conclusions about the amount of undetected baryonic matter required should be made using various disk models. If you know of any such studies that are peer-reviewed, I'm interested.

I've even seen an old paper by a supporter of non-baryonic CDM halos that admits that it is not needed to explain the rotation curves of many galaxies.


Yeah, did you miss the part about the foreground galaxy being unusual, because of the extent of the dust? The " We explore the radial and spatial distribution and the inferred extinction law of the dust in a smaller foreground spiral, which displays an extent of dust hitherto unseen in backlit galaxies." Which means previous galaxies that were backlit, didn't have as much dust as this one. Meaning observations don't support lots of dust outside the optical disk and backlit HI would be seen if there was a lot of it. Some of it has been seen, in backlit galaxies, but not the amount you seem to think there is.

No, I did not miss that. I don't draw the conclusion that this galaxy is unusual. Please read what you quoted carefully. It does not actually claim that other galaxies have less dust. The overlap in this case is very special, at least in comparison to other cases I have seen. The background galaxy is large and the illumination around the center is uniform and happens to be in just the right place to show the extent of the dust in the smaller foreground galaxy. If you know of other cases like this, bring them on.


Contrary to what you seem to think, this has been taken into account. From the paper:"The interstellar matter (ISM) extends to large radii in the form of atomic hydrogen (HI) but thus far there is little direct evidence of dust beyond the optical disk..."

Key words here are "thus far". It's very hard to see in a cold dark place. If you look to the right of the small galaxy in the photo, no dust is visible. I guess the photo is part of the "little direct evidence" referred to, but it's sure a nice piece.


Yeah, but, again from the paper: "In contrast, backlit dust can be detected independent of its temperature."

Yes, but such opportunities to study such a well back lit galaxy are very rare. In any case, it's very interesting that there is dust that far out. Dust requires metals which may mean that products of stars in the luminous parts have migrated outward and formed clouds, most likely predominantly H2. Now if virgin matter still exists in galaxies, it made reside very far from the luminous parts and the dust as well. Virgin (dustless) material being very cold H2 would be near impossible to detect.


Because there just isn't enough baryonic mass observed.

Yes because it's too hard to detect. Kind of like non-baryonic matter being so far impossible to detect.


Oh, by the way, this paper.... can't be used, if you using any of the other ones above as this one is incompatible with the ones above. So which one is it? You need to pick what you think is the problem and stick with it. Just because someone may not understand or doesn't like what current thought is, and writes a paper on it, doesn't mean there is actually anything to it.

Not sure which paper you are trying to eliminate. I think the problem is probably a combination of things. Probably the GR argument has validity. It is supported by other papers (although one minimizes the effect to still require non-baryonic matter). Studies to determine how much normal dark matter exists may be mistaken in their conclusions. For example, much has been made of the MACHO studies, but they seem to have the problem that they are looking in the wrong place. Unfortunately it is very hard to see anything far away and cold and dark in the right direction (in the galactic plane). A constant ratio of M/L is probably wrong and therefore the assumption that density falls off exponentially from the center is probably wrong as well.

TooMany
2011-Nov-06, 01:08 AM
You are looking at one thing, in isolation. My point was that it is irrelevant if your baryonic matter fits one bit of evidence as well as the CDM model. What matters is how it fits into the big picture too. It doesn't matter if you find a hoof print in your bedroom if the door is too small for a horse.

If you insist on killing two birds with the same stone, you are likely to fail to kill either.

Your conclusion here is fallacious. You CAN address each problem in isolation. This may be a reason that astronomers have ended up where they are - looking for a mysterious kind of matter. You seem unwilling to separate problems that may require different solutions because you want to prove the one solution that you are married to. Theory cannot trump observation. We do not need to solve cosmological problems in order to investigate and even solve the galactic rotation problem any more than we need BBT theory to explain the orbit of the earth around the Sun.

Furthermore, GR and quantum theory both work, but not together and as yet we have rejected neither.


We've had this argument before. Not going to comment, not going to get sucked in. You want to argue this go to the ATM section and write a full description of the ideas you feel confident enough to defend.

This "Against the Mainstream" stuff is a childish game that you use to clear the discussion space of ideas that you don't like. We are taking about mainstream science here. I am simply arguing that the possibility that the rotation curves are consistent with GR and baryonic matter has not been eliminated, just because astronomers cannot see the dark matter. You get your feathers up because you don't like the challenge it represents to the story you believe. You argue as though the existence of more baryonic matter to account for the rotation curves has been proved impossible, in spite of direct evidence of previously unseen dark baryonic matter.

You want me to believe in something never detected. I want you to consider that we may very well detect more of what we already know to exist and thereby firmly nail down an explanation of galactic rotation that allows us to move on with more confidence with GR and what we actually know about matter. That would be a huge step forward. Yes it would create other problems, but that's how progress gets made.

pzkpfw
2011-Nov-06, 01:34 AM
...
This "Against the Mainstream" stuff is a childish game that you use to clear the discussion space of ideas that you don't like. We are taking about mainstream science here. I am simply arguing that the possibility that the rotation curves are consistent with GR and baryonic matter has not been eliminated, just because astronomers cannot see the dark matter. You get your feathers up because you don't like the challenge it represents to the story you believe. You argue as though the existence of more baryonic matter to account for the rotation curves has been proved impossible, in spite of direct evidence of previously unseen dark baryonic matter.

You want me to believe in something never detected. I want you to consider that we may very well detect more of what we already know to exist and thereby firmly nail down an explanation of galactic rotation that allows us to move on with more confidence with GR and what we actually know about matter. That would be a huge step forward. Yes it would create other problems, but that's how progress gets made.

No, it's not a childish game, it's the way this part of the forum works. The Q&A forum is for asking a question and getting an answer within the bounds of mainstream, currently understood science. It is not the place to propose alternate theories, and if you wish to push your idea, you must do it in the ATM forum. That is the place on BAUT where you get to make the case, not here.

Shaula
2011-Nov-06, 07:50 AM
We do not need to solve cosmological problems in order to investigate and even solve the galactic rotation problem any more than we need BBT theory to explain the orbit of the earth around the Sun.
Yeah. We do. You missed my point entirely, or chose to ignore it. If your theory requires a configuration of matter for which we have no mechanism for it to form, if it requires that another theory (which is a good one backed up by evidence and models) be thrown out, if it requires us to rebuild from the ground up then it is not unreasonable to say that the balance of probabilities is against said theory. CDM models work when CDM is injected into the universe right at the start and allowed to evolve according to rules we understand. Your model requires a lot of tweaks to get it to match observations. More tweaks than CDM. So CDM is preferred. Come up with a broader model that explains the non-observation of the clouds and how they formed, how they are stable, why we cannot find them in clusters and so on and you'd be on to a genuine alternative theory.

Edit: BTW my comment here does NOT mean that effort should not be spent questioning the mainstream and trying out new models. It does, however, mean that outside these activities the answer to the question "what is the mainstream" should not be muddied by lots of theories with less evidence.

I am not wed to dark matter BTW. I'd rather it wasn't there. The problem is that evidence so far is stronger for CDM. That is all there is to it. So I can put aside my distaste and work with the best current model. Which may change. I'm old enough to have been around through some of the MACHO/HDM/WDM and so on models a decade ago. I remember dark energy being discovered and my disbelief and dislike of that. But I am just enough of a scientist to accept the consensus of the community over my own gut feelings and prejudices.

antoniseb
2011-Nov-06, 11:12 AM
... If your theory requires a configuration of matter for which we have no mechanism for it to form, if it requires that another theory (which is a good one backed up by evidence and models) be thrown out...
The model that TooMany is proposing has the flaw that all forms of cold baryonic matter (*) have absorption bands in the deep infrared (and most also in the near infrared and optical) and we do not see this absorption. The column density is near zero, but for his model to work, it would make those bands opaque around the Milky Way. So, TooMany doesn't have a viable solution, only a complaint that he doesn't like Cold Dark Matter because we haven't identified what it is made of yet.

* except free neutrons, but they decay into protons and electrons in a matter of minutes.

Shaula
2011-Nov-06, 11:25 AM
Ah, I'd assumed that he meant that the baryonic matter was distributed in just such a way as to make it very hard or impossible to observe spectroscopically. I guess what I was trying to say was that if, even if, this model could explain away DM it just replaces it with another problem - how the heck did the matter get into that configuration and why does the CDM model work better for the early universe?

For the record I think that the baryonic models are so heavily constrained by observations that they are basically ruled out. But even if you argue that they are not then that is just the first of your problems!!

TooMany
2011-Nov-06, 03:17 PM
No, it's not a childish game, it's the way this part of the forum works. The Q&A forum is for asking a question and getting an answer within the bounds of mainstream, currently understood science. It is not the place to propose alternate theories, and if you wish to push your idea, you must do it in the ATM forum. That is the place on BAUT where you get to make the case, not here.

It's not my theory. It's a theory and a very obvious one. Is there a definition presented of what the "bounds of mainstream" are? I'm not suggesting a new theory of gravity or a new kind of matter. In fact what I'm really trying to determine is

1) how confident can we be about constraints on additional baryonic matter, purely from observational evidence?
2) what assumptions are made about the form of dark baryonic matter to argue that it should have been detected but has not been?
3) if you consider a distribution of dark baryonic matter like that suggested by the back lit galaxy, how much additional baryonic matter is needed to explain the rotation curves?
4) which galaxies studied require large amounts of dark matter (say > 4X) to explain rotation and which do not? What are the statistics?

Cougar
2011-Nov-06, 03:25 PM
Unfortunately it appears the majority of papers start with the assumption that the DM is distributed spherically...

Well, some papers may take that as a given, but only because previous papers determined that the DM must have that distribution based on the orbital dynamics of galaxy members.

Cougar
2011-Nov-06, 03:36 PM
Your conclusion here is fallacious. You CAN address each problem in isolation.

Any viable theory has to be consistent with all known observations and findings. If you don't kill all the birds (observations) with one stone (theory), then your stone is deficient.

Cougar
2011-Nov-06, 04:19 PM
It's rather difficult to find papers that assume that dark stuff that we cannot see is just plain old matter and derive sensible distributions to account for rotation curves.

Are you kidding? There have been numerous massive research programs using independent methods to find baryonic matter that would explain the flat rotation curves. Some was found, but not nearly enough. The dark matter hypothesis is mainstream, but not because scientists "like" it or "believe" in it. It is because the observations force them to accept it. Of course, all theories are tentative and provisional, considering unknown future observations. Some are more tentative than others.

Cougar
2011-Nov-06, 04:30 PM
Here's an interesting photo of overlapping spirals that lends some direct support to the possibility that large amounts of baryonic dark matter surround the visible disks of spiral galaxies....

Do you think that any kind of matter surrounding the visible disk of spiral galaxies has any appreciable effect on the rotation curves of those galaxies?

TooMany
2011-Nov-06, 04:36 PM
Yeah. We do. You missed my point entirely, or chose to ignore it. If your theory requires a configuration of matter for which we have no mechanism for it to form, if it requires that another theory (which is a good one backed up by evidence and models) be thrown out, if it requires us to rebuild from the ground up then it is not unreasonable to say that the balance of probabilities is against said theory.

No I have not missed that point. In fact you are making my point. What you are saying is that your theory is right and then concluding that baryonic dark matter is impossible as an explanation. What I am saying is let's forget about theories of creation of the universe and just do observations and analysis of the local group of galaxies.

Independent of other theories, let's carefully analyze a very simple theory based on things we know to exist and the theory of gravity that we have some confidence in. What do we find when we do that analysis as carefully as possible? What galactic models are possible, independent of assumptions about how much baryonic matter can exist derived from cosmological theories?

I have the following reasons to be uncomfortable with the current LCDM conclusions about galactic rotation:

1) The cold dark baryonic matter is very difficult to detect. It could be in small dense clouds that cause extreme scattering events, as one possibility.
2) Until recently, Newtonian approximations have been exclusively used to model galactic rotation. Some GR experts say that this leads to incorrect results. Thus we may be drawing conclusions based on an incorrect analysis.
3) The argument that M/L ratio is constant is seriously challenged by the photo of a back lit galaxy.
4) The CDM theory is running into the "cuspy halo problem" and it's getting worse with recent studies of dwarf galaxies.
5) In spite of four decades of looking, the proposed invisible matter has not been detected. Moreover the LHC experiments are closing in on eliminating the proposed models for the existence of these particles. (I'm am not claiming the possibility of the existence of such particles has been eliminated. It can never be eliminated.)

I am interested in what we really know about these things. I've been told that all the papers I sited are suspect. So where are the papers that do a thorough, peer-reviewed analysis of the possibility of galaxies being composed of baryonic matter, from direct observation, rather than from theoretical cosmological arguments?


CDM models work when CDM is injected into the universe right at the start and allowed to evolve according to rules we understand. Your model requires a lot of tweaks to get it to match observations. More tweaks than CDM. So CDM is preferred. Come up with a broader model that explains the non-observation of the clouds and how they formed, how they are stable, why we cannot find them in clusters and so on and you'd be on to a genuine alternative theory.

Again, that's the problem. You are constraining your analysis of galactic rotation curves to fit a cosmological theory. It is perfectly legitimate to propose a model for galaxies to explain their behavior without explaining how they formed, how much baryonic matter is in the universe and so on.

Because you believe that your theory must be right, perhaps you fail to thoroughly investigate other (rather obvious) possibilities to explain the galactic dynamics.

Don't you see? You are trying to exclude a theory about one thing because it does not explain another. It does not have to. It just has to explain that one thing well. Other things can have other explanations.


Edit: BTW my comment here does NOT mean that effort should not be spent questioning the mainstream and trying out new models. It does, however, mean that outside these activities the answer to the question "what is the mainstream" should not be muddied by lots of theories with less evidence.

Thanks for including that caveat.

This is a personal opinion, but the current state of astronomy seems very far from the "precision cosmology" that has been claimed. After all, this current theory requires that 80% of mass is a new, undetected form of matter. Arguments using LCDM are made about many things, such as evolution of galaxies, acceleration of expansion and the like. However they are rather muddy because of the large number of assumptions involved and because the precision of the knowledge we do have is limited. In fact the conclusions reached in most papers assume the correctness of LCDM. For example, LCDM assumptions drive the selection process and interpretation of the supernova evidence. So in my mind to portray to the public that we have a very nice, virtually irrefutable theory of everything is a bit disingenuous.


I am not wed to dark matter BTW. I'd rather it wasn't there. The problem is that evidence so far is stronger for CDM. That is all there is to it. So I can put aside my distaste and work with the best current model. Which may change. I'm old enough to have been around through some of the MACHO/HDM/WDM and so on models a decade ago.

We'll I'm kind of old, so I have seen theories come and go. Perhaps with that perspective I'm less attached to the latest one. Seeing astronomers change there minds about things so frequently over the past five decades I do not expect the current theory to stand.


I remember dark energy being discovered and my disbelief and dislike of that. But I am just enough of a scientist to accept the consensus of the community over my own gut feelings and prejudices.

I hope that I can be that objective as well. However, if consensus were the means of scientific progress then we would still believe that the Sun revolves around the earth.

TooMany
2011-Nov-06, 04:54 PM
Are you kidding? There have been numerous massive research programs using independent methods to find baryonic matter that would explain the flat rotation curves. Some was found, but not nearly enough. The dark matter hypothesis is mainstream, but not because scientists "like" it or "believe" in it. It is because the observations force them to accept it. Of course, all theories are tentative and provisional, considering unknown future observations. Some are more tentative than others.

I read a paper summarizing the MACHO results but I was left wondering what they could actually conclude by looking for such things through a line of site to LMC and SMC. Many conclusions I have seen about molecular hydrogen seem to based on other assumptions. E.g. we can tell by looking for CO. The distribution of HI is the same as H2. There was a paper published in 1999 I think claiming detection of large amounts of slightly warm H2 in a couple of edge-on galaxies. Was that shown to be incorrect? You see, it's not so obvious how much stock to put in the claim that the baryonic matter is simply not there. If you would like to site some papers that make a strong argument, please do. Also, if you can site some acceptable papers that examine baryonic models for galactic rotation curves, I am very much interested in reading them.

TooMany
2011-Nov-06, 05:03 PM
Do you think that any kind of matter surrounding the visible disk of spiral galaxies has any appreciable effect on the rotation curves of those galaxies?

Yes, based on a few papers that I've seen it appears that a disk distribution of dark matter beyond the luminous parts of galaxies could account for the rotation curves. If you can site papers that show it cannot, then please do.

Shaula
2011-Nov-06, 05:16 PM
Again, that's the problem. You are constraining your analysis of galactic rotation curves to fit a cosmological theory. It is perfectly legitimate to propose a model for galaxies to explain their behavior without explaining how they formed, how much baryonic matter is in the universe and so on.
OK then we are going to have to disagree. I think that if you propose a model for something, no matter how well it works for that one narrow case, if you have to propose that all your other theories are overturned (most of which have strong evidence) then it is a good sign you are going wrong. It has to fit into the wider model. Or you have to propose something more that just "this fits this case, so it must be right".

However, if consensus were the means of scientific progress then we would still believe that the Sun revolves around the earth.
Nope. Maybe I should elaborate on what I meant by consensus. What I meant by consensus was that when I was building a theory, teaching a subject or doing the calculations I use the current best theories, as accepted by the majority of my peers, to build on. I do not insist on using my own pet theories and ideas until I have amassed enough evidence to convince enough people that I have a viable model. In short I focus on producing or using the best available theories. Not the ones that 'seem right' to me. I am not arguing for a tyranny of the masses. Other views can and should be tested. When the balance of evidence tips and they are viable they can replace the mainstream and be taught. But not before.

Cougar
2011-Nov-06, 05:43 PM
What galactic models are possible, independent of assumptions about how much baryonic matter can exist derived from cosmological theories?

The amount of baryonic matter is not "assumed." It is tightly constrained based on known physics. You can't just throw out a solid finding because it is inconsistent with a theory you're trying to support.


So where are the papers that do a thorough, peer-reviewed analysis of the possibility of galaxies being composed of baryonic matter, from direct observation, rather than from theoretical cosmological arguments?

I suggest a google search. The projects seeking a baryonic answer each look for a particular kind of baryonic answer, so no single paper rules out all potential baryonic explanations. Taken together, however, the "baryonic answer" is not forthcoming.


It is perfectly legitimate to propose a model for galaxies to explain their behavior without explaining how they formed, how much baryonic matter is in the universe and so on.

But it would be a worthless model if it is contradicted by other observations and confirmed findings.


You are trying to exclude a theory about one thing because it does not explain another. It does not have to. It just has to explain that one thing well. Other things can have other explanations.

A viable theory should not be inconsistent with a body of well-known physics.


After all, this current theory requires that 80% of mass is a new, undetected form of matter.

Not to raise your blood pressure, but it's much worse than that when you throw in dark energy.


Arguments using LCDM are made about many things, such as evolution of galaxies, acceleration of expansion and the like.

I'm fairly well-read on these matters. I've never read that the acceleration of the expansion has anything to do with explaining cold dark matter. Can you explain?


However they are rather muddy because of the large number of assumptions involved...

What large number of assumptions? DM is presumed based on observed galactic rotation curves. Beyond that, more DM is needed based on observed cluster dynamics.


For example, LCDM assumptions drive the selection process and interpretation of the supernova evidence.

I thought we were talking about cold dark matter (CDM). The "L" in "LCDM" was placed there because of the supernova evidence, not the other way around, as you represent.


So in my mind to portray to the public that we have a very nice, virtually irrefutable theory of everything is a bit disingenuous.

Nobody does this.


Seeing astronomers change there minds about things so frequently over the past five decades I do not expect the current theory to stand.



"One can imagine a category of experiments that refute well-accepted theories, theories that have become part of the standard consensus of physics. Under this category I can find no examples whatever in the past one hundred years." -- Steven Weinberg (http://en.wikipedia.org/wiki/Steven_Weinberg)

Cougar
2011-Nov-06, 05:48 PM
Yes, based on a few papers that I've seen it appears that a disk distribution of dark matter beyond the luminous parts of galaxies could account for the rotation curves. If you can site papers that show it cannot, then please do.

Principia (http://en.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematica) - Isaac Newton, published in 1687.

TooMany
2011-Nov-06, 07:50 PM
The amount of baryonic matter is not "assumed." It is tightly constrained based on known physics. *You can't just throw out a solid finding because it is inconsistent with a theory you're trying to support.

I suggest a google search. The projects seeking a baryonic answer each look for a particular kind of baryonic answer, so no single paper rules out all potential baryonic explanations. Taken together, however, the "baryonic answer" is not forthcoming.

You can wave your hands around like that but it's not very helpful. If you want to promote your mainstream theory then why don't you site some specific papers? It is rather sad, if you are correct, that there is no peer-reviewed paper summarizing the evidence that further baryonic is not to be found.

I've been looking for anything resembling that for some time. I'm willing to look more, but I thought because you folks are so sure about the evidence that you would easily site some of the papers accepted by the mainstream as proof of the non-existence of this matter. I truly want to read them.

What solid finding am I throwing out?


But it would be a worthless model if it is contradicted by other observations and confirmed findings.

If you are referring to findings like cluster masses or primordial abundances demanding something about rotation curves, then your reasoning involves common fallacies. Look up "fallacy of composition", "fallacy of division" and "fallacy of the single cause".


A viable theory should not be inconsistent with a body of well-known physics.

Yes, I agree. So what's wrong with using the existing type of matter we know about and accepted theory of gravity to attempt an explanation of galaxy rotation curves?


Not to raise your blood pressure, but it's much worse than that when you throw in dark energy.

Not sure what your point is here, but is anyone really happy about that conclusion?


I'm fairly well-read on these matters. I've never read that the acceleration of the expansion has anything to do with explaining cold dark matter. Can you explain?

What large number of assumptions? DM is presumed based on observed galactic rotation curves. Beyond that, more DM is needed based on observed cluster dynamics.

The point I was trying to make is that many conclusion that are published (and accepted) in mainstream astronomy are based on many assumptions, e.g. a certain GR model for expansion, quantities of obscuring cosmic dust, models of stellar development and so on. Often such studies (I believe the supernova study is one) begin by using the relativistic expansion dimming and dust estimates to choose the events that are included in the analysis. Therefore conclusions may be very sensitive to models. The universe is a very complicated place. While on very large scales it may be homogeneous, in any locality is it anything but. All these things must be taken into consideration and that is a very difficult task. Look how long for example the analysis of the Planck data is taking. It is not a simple matter to attempt to see through our galaxy and those beyond it. In summary, some conclusions must be viewed with some amount of skepticism, depending of the assumptions involved and errors in measurement.

Also, I specifically mentioned that I usually see estimates of baryonic dark matter (H2) based on tracers like CO and HI. That's an example of where you start getting into assumptions. In particular the assumption that things we cannot detect are distributed precisely like those things that we can detect. This sort of assumption also shows up in the constant M/L ratios used to estimate the amount missing matter required.


I thought we were talking about cold dark matter (CDM). The "L" in "LCDM" was placed there because of the supernova evidence, not the other way around, as you represent.

Yes I know that. I just used LCDM as the current name for the BB theory. I did not intend such a representation.


So in my mind to portray to the public that we have a very nice, virtually irrefutable theory of everything is a bit disingenuous.

Nobody does this.

Well then why do people keep telling me that I have some strange theory that is muddying the water of the correct one?




"One can imagine a category of experiments that refute well-accepted theories, theories that have become part of the standard consensus of physics. Under this category I can find no examples whatever in the past one hundred years." -- Steven Weinberg (http://en.wikipedia.org/wiki/Steven_Weinberg)


I would suggest that Steven has not looked very hard, if he's including cosmology. But what is your point, that your theories are likely irrefutable? Besides I have not conjectured anything that would break the physics that we really know about. Theories in cosmology are simple not in the category of things like, GR, quantum theory and particle theory. By the way, this argument is called "appeal to authority".

Cougar
2011-Nov-06, 07:58 PM
You can wave your hands around like that but it's not very helpful.

I'm just recalling what I've read. I don't feel like doing your research for you at this time.

TooMany
2011-Nov-06, 08:10 PM
I'm just recalling what I've read. I don't feel like doing your research for you at this time.

Cougar, sorry but that is a complete cop out. You demand proof from me. You want me to show you equations and papers etc. on an ATM thread. But you are unwilling to subject any of that evidence which you claim to exist in abundance to scrutiny?

I put forward what I was able to find about galactic rotation curves without the assumption of a spherical distribution of an "unknown type of matter". I was told that those papers are unreliable (implication - wrong). So where is the correct analysis? Please, if you know, tell me?

If you cannot back up your broad claims of proof that there is no more baryonic matter to be observed, then stop making them.

antoniseb
2011-Nov-06, 08:12 PM
...The point I was trying to make is that many conclusion that are published (and accepted) in mainstream astronomy are based on many assumptions, e.g. a certain GR model for expansion, quantities of obscuring cosmic dust, models of stellar development and so on. ...

Please try to stay on the topic of the original post, and title of the thread. This thread has veered way off the original question... which was answered pretty early on in the thread. TooMany, you are relatively new here, and as sometimes happens seem to feel that you don't like the rules and culture of this forum, and choose not to abide by them. Please work a little harder at fitting in, and respecting the amount of work you are asking people to do with your questions. If you want to support non-mainstream topics, please take it to ATM. If you don't have the stamina for holding up your side of an ATM discussion (and the evidence so far is that you do), just accept the answers. Don't rail about close-minded scientists here.

TooMany
2011-Nov-06, 08:18 PM
Principia (http://en.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematica) - Isaac Newton, published in 1687.

Now really Cougar. Try that one out on a forum called "FTM" (For the Mainstream), which come to think of it is this forum. Care to explain how Isaac Newton's theory ruled out this possibility? Perhaps you would rather just leave the implication that it does backed only by your say so? Show us!

TooMany
2011-Nov-06, 08:33 PM
Please try to stay on the topic of the original post, and title of the thread. This thread has veered way off the original question... which was answered pretty early on in the thread. TooMany, you are relatively new here, and as sometimes happens seem to feel that you don't like the rules and culture of this forum, and choose not to abide by them. Please work a little harder at fitting in, and respecting the amount of work you are asking people to do with your questions. If you want to support non-mainstream topics, please take it to ATM. If you don't have the stamina for holding up your side of an ATM discussion (and the evidence so far is that you do), just accept the answers. Don't rail about close-minded scientists here.

antoniseb, as administrator you can do whatever you please with this thread. It's true that I have strayed from the original poster's comment (from whom we've heard very little since). If you would like to use that argument to shut down this thread like the last one, I cannot stop you.

I had hoped that a discussion here would bring out the papers that support the mainstream views about this subject, but they are apparently not forthcoming, unfortunately. I am not "rail"ing about close-minded scientists. I am asking about the "acceptable" papers that study models of galaxies without non-baryonic dark matter. Surely someone legitimate has studied such models. The silence (paper wise) is not very illuminating. All I get is "most scientists believe"... I'm asking why they believe it and, more than that, I'd like to read the papers that you feel back this up myself rather than just hearing your interpretations. Is that too much to ask from the mainstream?

The posters are willing to go on and on about what scientist know, but not willing to stick their necks out and site a few good convincing papers?

Cougar
2011-Nov-06, 09:02 PM
If you are referring to findings like cluster masses or primordial abundances demanding something about rotation curves, then your reasoning involves common fallacies. Look up "fallacy of composition", "fallacy of division" and "fallacy of the single cause".

Well, beside the fact that the value of that if-then statement is "false"....


So what's wrong with using the existing type of matter we know about and accepted theory of gravity to attempt an explanation of galaxy rotation curves?

You don't think this has been thought of before? This has been pondered and experimented upon by some of the best human minds on the planet for more than 50 years. They've looked. They have not found. There's not near enough baryonic matter out there. If you devise a new detection method to identify up to 10 times more mass than is already detectable in all the stars, nebulae, gas, dust, and central supermassive black hole, I'll write it up for you if I can be second author. :whistle:


Not sure what your point is here [dark energy], but is anyone really happy about that conclusion?

An entirely new area of research? I'm elated.


Also, I specifically mentioned that I usually see estimates of baryonic dark matter (H2) based on tracers like CO and HI. That's an example of where you start getting into assumptions.

I haven't looked into this. Is there something wrong with that assumption? Or possibly, are you taking this practice out of context from what the observers were intending?


By the way, this argument is called "appeal to authority".

A scientist appeals to the facts. Not always, but I tend to think that most Nobel Laureates do not misrepresent the facts.

tusenfem
2011-Nov-06, 09:34 PM
If you cannot back up your broad claims of proof that there is no more baryonic matter to be observed, then stop making them.

TooMany, please know that ADS is your friend in finding papers (http://esoads.eso.org/cgi-bin/nph-abs_connect?db_key=AST&db_key=PRE&qform=AST&arxiv_sel=astro-ph&arxiv_sel=cond-mat&arxiv_sel=cs&arxiv_sel=gr-qc&arxiv_sel=hep-ex&arxiv_sel=hep-lat&arxiv_sel=hep-ph&arxiv_sel=hep-th&arxiv_sel=math&arxiv_sel=math-ph&arxiv_sel=nlin&arxiv_sel=nucl-ex&arxiv_sel=nucl-th&arxiv_sel=physics&arxiv_sel=quant-ph&arxiv_sel=q-bio&sim_query=YES&ned_query=YES&adsobj_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=AND&title=baryonic+dark+matter&txt_logic=OR&text=&nr_to_return=200&start_nr=1&jou_pick=NO&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1). The link goes to all peer reviewed papers with the key words "baryonic, dark, matter" in the title.

TooMany
2011-Nov-06, 10:52 PM
TooMany, please know that ADS is your friend in finding papers (http://esoads.eso.org/cgi-bin/nph-abs_connect?db_key=AST&db_key=PRE&qform=AST&arxiv_sel=astro-ph&arxiv_sel=cond-mat&arxiv_sel=cs&arxiv_sel=gr-qc&arxiv_sel=hep-ex&arxiv_sel=hep-lat&arxiv_sel=hep-ph&arxiv_sel=hep-th&arxiv_sel=math&arxiv_sel=math-ph&arxiv_sel=nlin&arxiv_sel=nucl-ex&arxiv_sel=nucl-th&arxiv_sel=physics&arxiv_sel=quant-ph&arxiv_sel=q-bio&sim_query=YES&ned_query=YES&adsobj_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=AND&title=baryonic+dark+matter&txt_logic=OR&text=&nr_to_return=200&start_nr=1&jou_pick=NO&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1). The link goes to all peer reviewed papers with the key words "baryonic, dark, matter" in the title.

Hi, thanks for that link. I've mainly been using arXiv.

Tensor
2011-Nov-06, 11:25 PM
You can wave your hands around like that but it's not very helpful. If you want to promote your mainstream theory then why don't you site some specific papers? It is rather sad, if you are correct, that there is no peer-reviewed paper summarizing the evidence that further baryonic is not to be found.

There are plenty of peer reviewed papers. I don't know about the others, but I've spent up to two hours looking for papers for you, before posting. You're the second person we've had here in the last month that's demanded we find papers for them, and I'm sorry, but I don't do demands. You present papers that don't even pass peer review and waste my time looking through them. Why don't you spend a bit more time looking at the papers and find possible problems with them, not just look at them, find they agree with you, and list them as showing there is a problem with the mainstream model? Especially when they don't even agree with each other.


I've been looking for anything resembling that for some time. I'm willing to look more, but I thought because you folks are so sure about the evidence that you would easily site some of the papers accepted by the mainstream as proof of the non-existence of this matter. I truly want to read them.

The evidence is spread across papers, disciplines, and observations. Cosmologists just didn't go oh, look, rotation curves for galaxies don't match our gravitational equations, we'll just put some unknown, fantasy particle around galaxies, in just the right positions, without checking to see if we can detect it there. And, by the way, we don't care about matching any other observations. They take this observation, match it with this other theory, then make a reasonable assumption, run monte carlo simulations, so they can make a prediction, to see if another observation matches that prediction. If it does, they get to start over from there and continue on. You seem to want one observation, based on one hypothesis, no matter how fringe, as long as that hypothesis isn't the current dark matter idea. Sorry, but it doesn't work like that, no matter how much you dislike it.


Theories in cosmology are simple not in the category of things like, GR, quantum theory and particle theory.

This is the silliest thing I've ever heard. What do you think is used to come up with cosmological theories, psychology? The idea for inflation came, not from an astrophysicist, but from a particle physicist with an idea to get rid of magnetic monopoles. The energy for inflation comes from the freezing out of the other forces, quantum theory. Nuclearsynthesis abundances come from the coupling constants in quantum theory. Comoving coordinates that explain cosmological redshift comes from GR. One thing that is laughable in all those papers you keep coming up with is that they have all (so far) implicitly accepted the Big Bang. Because all of them have used observational catalogues (be they star, galaxy, QSO, etc), whose brightness, size, distance (based on their red shift) etc, are based on ΛCDM model. Which is why we keep hammering you on whether or not the ideas you put for matches all observations. ΛCDM, while it does have a few problems here and there, they are not insolvable, as you seem to think. And the catalogues are based on it. Other interpretations are possible, but anyone wanting those other interpretations will have to do the work to reevaluate all the observations. Guess how many other I've seen do the work?


By the way, this argument is called "appeal to authority".

And your technique, on this matter, has been, what exactly?

TooMany
2011-Nov-07, 01:13 AM
Right now I'm not interested in theories of the creation of the universe, inflation etc., nor how well they do or don't work to explain various other things. I don't care if the non-baryonic matter's existence is required by cosmological theories. I'm trying to understand one problem, and yes deliberately without trying to make a theory of everything or assuming any particular cosmology.

I am focused on one seemingly simple issue:



Given our accepted theory of gravity, what galactic models without non-baryonic dark matter can explain the rotation curves and how much undetected baryonic matter is needed to account for the rotation.


Certainly this has been considered. I have found papers that address this, but I've been told that they don't "count". I've asked for help finding the papers that address this particular issue that do count, but I've received no help. So I am sifting through dozens of papers and have been for days.

And you know what, the papers I have found on this topic so far are either equivocal about the need for non-baryonic dark matter halo or deny that it's needed at all to explain the rotation curves.:confused:

P.S. Other papers I've encountered that do use the non-baryonic halo model consider only that model and it nuances in regard to galactic rotation curves.

Cougar
2011-Nov-07, 02:30 AM
I am focused on one seemingly simple issue:


Given our accepted theory of gravity, what galactic models without non-baryonic dark matter can explain the rotation curves and how much undetected baryonic matter is needed to account for the rotation.

As an initial matter, it's not just how much, but where it must be. It cannot all be in the nucleus, for example. That would describe a different rotation curve. To match the observed rotation curve, it must be throughout the disk, its density apparently dropping off as the inverse square of the radius. And it extends well beyond the disk; but the gravitational effect on the disk from all the mass exterior to the disk is approximately gravitationally balanced. Granted, Newton's closed-form solution in his Principia proving this exactly was a special case of this generalized problem, but I expect it still holds in the circumstance, within error bars. :)

Tensor
2011-Nov-07, 06:27 AM
Right now I'm not interested in theories of the creation of the universe, inflation etc., nor how well they do or don't work to explain various other things. I don't care if the non-baryonic matter's existence is required by cosmological theories. I'm trying to understand one problem, and yes deliberately without trying to make a theory of everything or assuming any particular cosmology.

I am focused on one seemingly simple issue:

And that is your problem, it's not simple. Period. End of discussion. You want it to be, but it isn't. Nothing can be considered in isolation. Oh, if you want, you can consider everything in isolation. But, if you do that, as soon as you try to put this piece together with this other piece, it flat doesn't work.


Given our accepted theory of gravity, what galactic models without non-baryonic dark matter can explain the rotation curves

Based on what? As explained by who? And why without non-baryonic dark matter? And, as accepted by who? It's not a problem with Young-Earth Creationists, it was all created less than 10,000 years ago. You've pointed out a group who thinks that GR along can explain it. None of the other GR experts out there think it can and antoniseb has explained why he doesn't think it's a good solution. I have problems with it myself. I also happen to have non-baryonic hypothesis, but I don't think you'd approve of my idea of a mass of invisible pink unicorns. I don't have any observational support, but, hey, you can't prove me wrong either. And I could even write it up and get it on vixra, which doesn't mean it's possible, but it would be an example of a scientific sounding paper. And as much as you don't want to, you have to consider what cosmology you're using, whenever you state a hypothesis. Simply because any kind of change in the parameters, changes the time, distance, brightness, all the Omegas, the Sne1 observations, which changes the galaxy observations,

What specifically are your requirements? You don't seem to have a problem with multiple possibilities, even when they are mutually exclusive. So, what exactly should we concentrate on? You complain about non-baryonic dark matter, yet when we point out that microlensing (not just in the Milky Way, but in other galaxies and galactic clusters) show that there 10-100 time more matter than is seen, and we don't see it, it can't something that'll interact electromagnetically. And, like it or not, HII, will interact electromagnetically. Either through absorption, emission, or scattering. And if any of that happens, we will see it, one way or another. You point out a GR possibility, but then won't even answer my question on how you knew the ideas in the paper were valid, other than it agrees with your sensibilities about not having any non-baryonic dark matter. Or, hey, how about the paper where they put a bunch of matter in the arms. Or the one where the matter goes in the area between the arms. Oh, I know, the one that extends it out past the optically visible disk, etc, etc, etc. Which one do you want us to use?


and how much undetected baryonic matter is needed to account for the rotation.

One of the reasons we may not be taking your objections seriously, is simply that you have been objecting to the current dark matter model, and then you ask a question like this? A question you should know if you object to the current model. Anyway, I think the current estimate is 90% of the mass of the Milky Way (and up to 90% in spirals, depending on the type) is tied up in dark matter. Which is why trying to explain it with HII isn't really an option.


Certainly this has been considered. I have found papers that address this, but I've been told that they don't "count".

And we've given you specific reasons why they don't count. Mostly what we've gotten back is, but I don't like the current dark matter idea and this agrees with me.


I've asked for help finding the papers that address this particular issue that do count, but I've received no help. So I am sifting through dozens of papers and have been for days.

And, exactly how long do you think it took them to learn what was needed to know what observations were needed? To perform the and sift through the observations, perform the calculations, and review everything required to write those papers? To get the ones that were published through peer review? I'm not even in the market to write any paper, and I know it took me months to get to the point where I felt comfortable with what I was reading and interpreting, and I'm still pretty much a newbie at this. And that doesn't even count the YEARS of study on other things that serendipitously make understanding this stuff easier. I've tried to get you papers that were pretty much unequivocal. Where the observations, facts, discussion, and conclusions were pretty much straight forward. And you say you've only been at it for days and expect some single illuminating paper? Good luck with that.


And you know what, the papers I have found on this topic so far are either equivocal about the need for non-baryonic dark matter halo or deny that it's needed at all to explain the rotation curves.:confused:

And, is there any difference between the two types of papers? In terms of peer review? Or whether they have been published? Or where they have been published? I asked that because I still am working on another reply for you. A more in depth review of the list of paper you gave us earlier. As I said, one was peer reviewed, another was published, but published in a periodical that does not require peer review to gets published, only, it appears, the editing required to ensure proper grammar, spelling and punctuation.


P.S. Other papers I've encountered that do use the non-baryonic halo model consider only that model and it nuances in regard to galactic rotation curves.

Mostly because, as we keep pointing out, it's the mainstream model. Most of the papers that describe observations (the catalogues of stars, galaxies, QSOs, Seyferts, etc) will assume the ΛCDM model (although they may mention using the concordance model at the beginning of the paper or catalogue).

TooMany
2011-Nov-07, 03:01 PM
You are not contributing anything concrete here, like a paper. I've already read enough papers to understand that the mainstream conclusions are nowhere near as well supported as you claim.

You are unwilling to give any credence to an interpretion of galaxy rotation curves that does not dovetail with theories about other things. Such a constrained view can blind you to reality.

The debate about rotation curves (and many other aspects of the currently popular theory of cosmology) is still alive. Existing data and methods of analysis are not yet good enough to be conclusive about most of the tenants of LCDM. The size of error bars in many papers is almost comical. It's clear that astronomers are trying to extract information from a very noisy background. It's a very difficult science.

Since you don't want to contribute anything in support of your claims, this discussion is pointless (as far as I'm concerned). Please find some other infidel to rail at; try ATM.

nota
2011-Nov-07, 03:30 PM
wow I thought this thread died after a few posts
then check it a week later and it is 2 pages and growing

my original questions were about if clouds of DM move as clouds
ie each DM bit effects all the other DM locally by their gravity
or each bit of DM has a orbit independent of all other DM bits
and why the anti-clumping but no force to cancel gravity induced clumps

I due understand DM doesNOT form solid lumps of DM as that requires bonds beyond gravity
but fail at the idea of non clumping [note clumps are different from lumps]
as if DM has mass and mass curves space
why does the mass and space curve of DM not form clumps [think clouds not solid lumps]
on one level a galaxy is a clump of mostly DM with a little normal matter in the center right ?
so is the nonclumping just a matter of scale ie no small clumps only big galaxy sized ones ?
or is the DM in a galaxy not bound to the galaxy and so free to leave the galaxy

tusenfem
2011-Nov-07, 03:39 PM
You are not contributing anything concrete here, like a paper. I've already read enough papers to understand that the mainstream conclusions are nowhere near as well supported as you claim.

You are unwilling to give any credence to an interpretion of galaxy rotation curves that does not dovetail with theories about other things. Such a constrained view can blind you to reality.

The debate about rotation curves (and many other aspects of the currently popular theory of cosmology) is still alive. Existing data and methods of analysis are not yet good enough to be conclusive about most of the tenants of LCDM. The size of error bars in many papers is almost comical. It's clear that astronomers are trying to extract information from a very noisy background. It's a very difficult science.

Since you don't want to contribute anything in support of your claims, this discussion is pointless (as far as I'm concerned). Please find some other infidel to rail at; try ATM.


ETA: Tone it down TooMany, this kind of comments will get you infracted.


Please present these papers that you think make your case. That would be one step to actually show what you are claiming is mainstream.
As it looks now, I have great doubts whether this should stay in Q&A and should not be better in ATM.

The papers you cited in your first post:
Feng & Gallo - published in Journal of Cosmology in another version as Gallo & Feng (doubtful journal)
Gallo & Feng - only in arxiv
Feng & Gallo - only in arxiv
Nicholson - only on astro-ph
de Melo & Rasende - publische in International Journal of Modern Physics A (unknown to me)
Mei, Xu & Yu - only in arxiv
Banhatti - proceedings IAU confernece poster (can hardly be called a paper, looking at it)
Banhatti - only on astro-ph
Soares - published in Rev. Mex. Astron. Astrofis.

So from the list only 4 are actually published in peer-reviewed journals, but in the dubious Journal of Cosmology, one in a conference proceedings where reviewing is much more loose than in real journals, and then two other not-really important journals. You may have to come up with more convincing sources. arxiv is nice to look at, however practically anyone can post there, ADS is much much better as you can actually choose to have peer reviewed papers.

So, either you show real, trusworthy mainstream papers that support your claim, or this is off to ATM.

nota
2011-Nov-07, 03:41 PM
speed of DM
is this stuff if it is and is stuff move at normal speeds or near light speed ?
or exactly at light speed like photons and some other small bits do ?

and or does the whole halo move in a relationship to the rotation of the visible part of a galaxy

antoniseb
2011-Nov-07, 03:46 PM
speed of DM
is this stuff if it is and is stuff move at normal speeds or near light speed ?
or exactly at light speed like photons and some other small bits do ?

and or does the whole halo move in a relationship to the rotation of the visible part of a galaxy

You can make an initial assumption that each Cold DM particle is moving in a highly elliptical orbit from the outer parts of the galaxy into the inner part of the galaxy. This assumption needs to be modified because its motion is being driven in a distributed many-bodied mass.
So the average speed near us will be about 300 km/sec.

nota
2011-Nov-07, 03:53 PM
referencing the recent nova on PBS on space

they look to be saying space is not empty at all
but has property's

so could space it's self be dark matter ?
or to rephrase
is dark matter just an effect of space's propertys in a huge gravity well like a galaxy
but not active on a local scale in our solar system

antoniseb
2011-Nov-07, 05:08 PM
referencing the recent nova on PBS on space ...
is dark matter just an effect of space's propertys in a huge gravity well like a galaxy
but not active on a local scale in our solar system

You might be mixing what you've heard about dark matter with dark energy.

Hornblower
2011-Nov-07, 05:18 PM
wow I thought this thread died after a few posts
then check it a week later and it is 2 pages and growing

my original questions were about if clouds of DM move as clouds
ie each DM bit effects all the other DM locally by their gravity
or each bit of DM has a orbit independent of all other DM bits
and why the anti-clumping but no force to cancel gravity induced clumps

I due understand DM doesNOT form solid lumps of DM as that requires bonds beyond gravity
but fail at the idea of non clumping [note clumps are different from lumps]
as if DM has mass and mass curves space
why does the mass and space curve of DM not form clumps [think clouds not solid lumps]
on one level a galaxy is a clump of mostly DM with a little normal matter in the center right ?
so is the nonclumping just a matter of scale ie no small clumps only big galaxy sized ones ?
or is the DM in a galaxy not bound to the galaxy and so free to leave the galaxy

I would say that absence of clumping is consistent with absence of non-gravitational interactions such as inelastic collisions or a property of being sticky. These hypothetical DM particles would be buzzing around like neutrinos but much more slowly. I would expect their motion to be similar to that of the halo stars which we do observe. On a smaller scale, the motions of stars in globular clusters would be similar.


referencing the recent nova on PBS on space

they look to be saying space is not empty at all
but has property's

so could space it's self be dark matter ?
or to rephrase
is dark matter just an effect of space's propertys in a huge gravity well like a galaxy
but not active on a local scale in our solar system That may be saying the same thing in different words. There appears to be a lot of "stuff" out there that defies detection by any non-gravitational means.

Suppose there is DM in our region of the galaxy that has 10 times the mass of the local stars but is uniformly dispersed. The lack of clumping forces and the high velocities prevent it from being concentrated locally around individual stars. The portion inside an outer planet's orbit, which is the only portion that would perturb the planet, would be so slight that its gravity would be vanishingly small compared to that of the Sun at that range.

ngc3314
2011-Nov-07, 05:41 PM
Here's an interesting photo of overlapping spirals that lends some direct support to the possibility that large amounts of baryonic dark matter surround the visible disks of spiral galaxies:

http://imgsrc.hubblesite.org/hu/db/images/hs-2008-33-a-large_web.jpg

Here's a paper that discusses this:

http://arxiv.org/abs/0810.2646v1


As a coauthor on that paper and additional papers on the subject going back to 1983 - no. Based on the dust charactaristics we can best measure in the Milky Way, the mass of grains needed to account for that absorption (and far-infrared emission) in the galaxies we can study with backlighting is in the range 10-50 million solar masses, less than 1% of the mass in gas we can easily detect and a trivial fraction of the visible baryonic mass.


One result of the Galaxy Zoo project to find more examples is that we have failed to find a case example of a luminous non-interacting spiral galaxy with significant dust beyond the optical disk (a few possible examples all seem to be tidally distorted with the dust following tidal arms). The example in the picture is dwarfish, and we hope to look for more extended dust in similar systems shortly.

Cougar
2011-Nov-07, 05:43 PM
referencing the recent nova on PBS on space... they look to be saying space is not empty at all

Right. Since 1998, space is thought to have a small energy component - dark energy.


so could space it's self be dark matter ?

No. At this point, dark energy is thought to be distributed evenly throughout all space. Dark matter is gravitationally distributed around galaxies and galaxy clusters. The way dark energy is distributed would not produce the observed way galaxies rotate. Nor would the amount of dark energy in the proximity of a galaxy, or even a cluster, be enough gravitationally to have any significant gravitational effect.

TooMany
2011-Nov-07, 06:01 PM
ETA: Tone it down TooMany, this kind of comments will get you infracted.

Just out of curiosity, "infracted" for what? Can you please explain?

pzkpfw
2011-Nov-07, 06:06 PM
No more off topic posts please. The proper way to ask this kind of question would be a PM to a mod, reporting a post so the question can go to all mods, or starting a thread in the feedback section. The answer is: mods can give a kind of penalty to members, for breaking rules. (Please go read the rules; start with 0 and 2). These are called "infractions" and carry points (the worse the offence, the more the points). The points add up, and can result in suspension or banning. Please don't reply to this in-thread; that'll just add more off topic posts to the thread.

Tensor
2011-Nov-07, 08:47 PM
As a coauthor on that paper and additional papers on the subject going back to 1983 - no. Based on the dust charactaristics we can best measure in the Milky Way, the mass of grains needed to account for that absorption (and far-infrared emission) in the galaxies we can study with backlighting is in the range 10-50 million solar masses, less than 1% of the mass in gas we can easily detect and a trivial fraction of the visible baryonic mass.

Dang it Bill, going back to look, I should have paid attention, to the names, when I looked at the paper. If I had, I would have asked you about it right away. But, I just went right into the paper. Thanks for your input.

TooMany
2011-Nov-08, 12:42 AM
Based on the dust charactaristics we can best measure in the Milky Way, the mass of grains needed to account for that absorption (and far-infrared emission) in the galaxies we can study with backlighting is in the range 10-50 million solar masses, less than 1% of the mass in gas we can easily detect and a trivial fraction of the visible baryonic mass.

Are you saying that it is only dust and nothing else? In other words it is not an indication of any substantial quantity of matter outside of the visible disk aside from the dust itself? Do we find most dust without gas in our galaxy?

ngc3314
2011-Nov-08, 03:00 AM
Are you saying that it is only dust and nothing else? In other words it is not an indication of any substantial quantity of matter outside of the visible disk aside from the dust itself? Do we find most dust without gas in our galaxy?

Not at all - dust can be an observationally cheap tracer of dense gas (the gas dominates over grains by mass factors 100-200 when we have enough data to say), especially in the inner regions of spirals. But the masses inferred for gas associated with this rare dust configuration is nothing particularly in excess of other ways of inferring gas masses (H I emission, CO as a molecular tracer) so it's not particularly evidence of how much dark mass might be there (except that this technique is sensitive to diffuse very cold dust that's even hard to pick out in the far-IR, so gives a separate limit).

TooMany
2011-Nov-08, 03:52 PM
Thanks. What do you make of this galaxy? A rare form of galaxy or perhaps a typical dwarf spiral?

It seems in some studies of galactic rotation an assumption is made that the M/L is constant radially and therefore the matter density falls off exponentially just as the light. It is then concluded that there must be some amount of dark matter to account for the continued flat rotation curve.

I've also seen many references to "maximum disk" which appears to be some other assumption about the matter distribution, that I haven't quite grasped. However, some papers seem to be saying that for many galaxies this model does not require large amounts of DM to explain the rotation.

Can you shed any light on this because I'm confused about the conclusions; perhaps many galaxies require little or no DM to explain rotation?

nota
2011-Nov-09, 02:22 AM
Right. Since 1998, space is thought to have a small energy component - dark energy.



No. At this point, dark energy is thought to be distributed evenly throughout all space. Dark matter is gravitationally distributed around galaxies and galaxy clusters. The way dark energy is distributed would not produce the observed way galaxies rotate. Nor would the amount of dark energy in the proximity of a galaxy, or even a cluster, be enough gravitationally to have any significant gravitational effect.

well on top of your DE filled space
I thought there are virtual particles too as a result of QM uncertainty
so a lot of somethings in a vacuum

if the virtual particles pop in they produce gravity
lots of VP's popping = extra gravity

Cougar
2011-Nov-09, 01:58 PM
if the virtual particles pop in they produce gravity
lots of VP's popping = extra gravity

One would think so. But they are there one instant and gone the next. How do you deal with that? AFAIK, scientists haven't figured out how to measure the effect of all these virtual particles throughout the vacuum of space. If there is any. When they tried to calculate the amount of energy VPs should contribute to empty space, they came up with the biggest wrong answer in the history of the planet. Their answer was 10120 too big. Needless to say, this remains an active area of research.

mikeg64
2011-Nov-12, 09:46 AM
Is it likely that the distribution of DM in galactic halos will probably have as many forms as there are galaxy structures and these forms are dependent on the rotation and morphology of specific galaxies.

chornedsnorkack
2011-Nov-12, 10:15 AM
Is it likely that the distribution of DM in galactic halos will probably have as many forms as there are galaxy structures and these forms are dependent on the rotation and morphology of specific galaxies.

Does dark matter depend on the rotation of light matter, or vice versa?

If the dark matter were moving relative to Sun, would you expect it to exert a force on the Sun against the direction of the relative motion?

mikeg64
2011-Nov-12, 10:44 AM
Does dark matter depend on the rotation of light matter, or vice versa?



Dark matter obeys conservation of angular momentum but this does not imply a dependency on the rotation of light matter. Any dependency would arise from the gravitational interaction? As I understand it dark matter is viewed as the kind of "scaffolding" of galactic structure. However, I presume that light matter works the other way also and influences the distribution of dark matter.




If the dark matter were moving relative to Sun, would you expect it to exert a force on the Sun against the direction of the relative motion?


I'm thinking about that one... think I need to look at the rest of the posts in this thread more carefully ...... pending:)

chornedsnorkack
2011-Nov-12, 12:05 PM
Dark matter particles would be expected to get deflected on passing the Sun...

Strange
2011-Nov-12, 02:15 PM
If the dark matter were moving relative to Sun, would you expect it to exert a force on the Sun against the direction of the relative motion?

As in something like viscosity? I think not, because that would require interaction other than gravitational. Dark matter flows through the Sun and the Earth (and us) as if they weren't there. (Apart from any gravitational effects.)

chornedsnorkack
2011-Nov-12, 02:38 PM
As in something like viscosity? I think not, because that would require interaction other than gravitational. Dark matter flows through the Sun and the Earth (and us) as if they weren't there. (Apart from any gravitational effects.)

But there are gravitational effects.

If dark matter particles approach the Sun, should they not be deflected on their unbound, hyperbolic orbits?

antoniseb
2011-Nov-12, 03:02 PM
But there are gravitational effects. If dark matter particles approach the Sun, should they not be deflected on their unbound, hyperbolic orbits?

As I mentioned above, each individual DM particle moves through the galaxy on its own, and very likely they move in ways similar to how Oort cloud comets move through our Solar System, in high elliptical orbits, with no particular orientation, and very little net rotation when looking at the whole pool of them. Now, yes, they do individually interact with the Sun, but given their random position as they pass the Sun, they should not produce an overall impact on the motion of the Sun (which I'm thinking is what you're getting at).

Another thing you might have been trying to get at is that those DM particles that happen to be orbiting close to the plane of the stars will interact with the stars and get their orbits randomized a little bit. Most will increase their minimum distance to the center of the galaxy, but some will go the other way.

Now, let me say, that if you were getting to looking for some net effect on the motion of the Sun and other stars as a piece of evidence about the hypothesis of how DM moves in the galaxy... that is a cool idea. I'll have to do some thinking and math to see what it would take for us to detect that effect.

One side note, there should be streams of dark matter from the merger of smaller galaxies with ours, and (for example), the star Arcturus is a star from such a stream, and we should be experiencing some DM from that inbound halo, which would have a different orientation than what I described above.

chornedsnorkack
2011-Nov-12, 03:21 PM
As I mentioned above, each individual DM particle moves through the galaxy on its own, and very likely they move in ways similar to how Oort cloud comets move through our Solar System, in high elliptical orbits, with no particular orientation, and very little net rotation when looking at the whole pool of them. Now, yes, they do individually interact with the Sun, but given their random position as they pass the Sun, they should not produce an overall impact on the motion of the Sun (which I'm thinking is what you're getting at).

To the contrary, they should.

If two dark matter particles approach the Sun on parallel paths, one to the right of Sunīs center, the other equal distance to the left, then both should be accelerated, relative to the Sun, as they approach the Sun. And then decelerated to exact same speed as initial - but no longer on parallel paths.
The particle to the right of Sun should start moving to the right, and the particle to the left of Sun should start moving to the right.

The changes in momentum to left and right would cancel out. But both the particles would also acquire momentum in forward direction!

If the dark matter halo has "very little net rotation", and Sun does have net rotation, then there should be few dark matter particles approaching the Sun from behind, and many approaching the Sun from the front and slowing it down.


Another thing you might have been trying to get at is that those DM particles that happen to be orbiting close to the plane of the stars will interact with the stars and get their orbits randomized a little bit. Most will increase their minimum distance to the center of the galaxy, but some will go the other way.

Also net rotation should be transferred from stars to dark matter.



Now, let me say, that if you were getting to looking for some net effect on the motion of the Sun and other stars as a piece of evidence about the hypothesis of how DM moves in the galaxy... that is a cool idea. I'll have to do some thinking and math to see what it would take for us to detect that effect.



Also note that while flattening of dark matter might indicate net rotation thereof, and orientation of axis, it would not show the direction of rotation!

ngc3314
2011-Nov-12, 04:09 PM
ANow, let me say, that if you were getting to looking for some net effect on the motion of the Sun and other stars as a piece of evidence about the hypothesis of how DM moves in the galaxy... that is a cool idea. I'll have to do some thinking and math to see what it would take for us to detect that effect.

The math has been worked out (in various approximations) and gets listed under "dynamical friction" - a net scattering of more massive particles "downward" in a larger overall potential, because random encounters are more likely to increase the energy of lower-mass particles. (One way to look at this is that the gathering of particles in a wake behind the star will make the gravity of the surrounding ocean of particles asymmetric and produce a net gravitational drag). The rate of energy exchange is obviously a key factor. The effect has been sought within the stars of globular clusters and among galaxies in clusters. Intuitively, in the outer parts of galaxies one would expect the stars to show a greater change in orbital radius than dark-matter particles, because there is so much more dark matter, while in the inner baryon-dominated regions, the effect wouldn't matter because there was too little dark matter. Hmm - wonder whether there might be a crossover radius of greatest effect?

chornedsnorkack
2011-Nov-12, 05:00 PM
The math has been worked out (in various approximations) and gets listed under "dynamical friction" - a net scattering of more massive particles "downward" in a larger overall potential, because random encounters are more likely to increase the energy of lower-mass particles. (One way to look at this is that the gathering of particles in a wake behind the star will make the gravity of the surrounding ocean of particles asymmetric and produce a net gravitational drag).
Only for massive particles which are moving relative to the ocean. And if the ocean moves, then the ocean can give energy to the massive particles.


Intuitively, in the outer parts of galaxies one would expect the stars to show a greater change in orbital radius than dark-matter particles, because there is so much more dark matter, while in the inner baryon-dominated regions, the effect wouldn't matter because there was too little dark matter.

But the absolute quantity of dark matter increases inwards.

Cougar
2011-Nov-12, 05:11 PM
The rate of energy exchange is obviously a key factor.

Plus the simple fact that there's so much more space than suns.


To the contrary, they should.

The "dark matter effect" is most detectable at the level of clusters and galaxies, where there's a lot of it, in aggregate. To scale that down to the level of a solar system, you've got to divide the effect you're talking about (on the sun) by a very large number, thus making the effect very small....

mikeg64
2011-Nov-13, 12:29 AM
Dark matter doesn't interact electromagnetically, it can't radiate excess energy, and can basically only cool by its gravitational interactions with normal matter, so it forms diffuse halos instead of clumping.

this is profound and makes me realise I can't quite get my head around the behaviour of dark matter why does your argument imply DM should form halos?

mikeg64
2011-Nov-13, 12:42 AM
Dark matter particles would be expected to get deflected on passing the Sun...

sure it would otherwise how would we able to explain then anomalous motion of galaxies! Then again if there was too much dark matter in our solar system (near enough to be deflected by the sun) then our solar system would not add up gravitationally would kepler then have arrived at his rules?

Guess this implies the requirement for DM halos.

In line with some of the other postings these low mass weakly interacting entities would pass through most things in our solar system... they're only effective, gravitationally when clumped...

is this why DM is clumpy?

Hornblower
2011-Nov-13, 01:16 AM
sure it would otherwise how would we able to explain then anomalous motion of galaxies! Then again if there was too much dark matter in our solar system (near enough to be deflected by the sun) then our solar system would not add up gravitationally would kepler then have arrived at his rules?
Suppose there is enough dark matter evenly distributed within a range of a hundred light years to be ten times the mass of all the stars in the same region. The amount inside the orbits of the outer planets would be a vanishingly small fraction of a solar mass, insufficient to observably change their orbital periods. In other words the Sun vastly overpowers the dark matter at planetary range.




Guess this implies the requirement for DM halos.

In line with some of the other postings these low mass weakly interacting entities would pass through most things in our solar system... they're only effective, gravitationally when clumped...

is this why DM is clumpy?