No Dark Matter in our part of the galaxy?

[TooMany]

Can you give some references, please?

Go to arvix.org. Type Pfenniger in the Author box, select Physics astro-ph.

I'm particularly interested in learning how helium can condense into solids.

Come on Nereid. That's a strawman, nobody said it could.

As I understand it, certain bacteria can form nucleation centres for snowflakes too.

However, the mechanisms for the formation of snowflakes in a high-temperature, high density oxygen-nitrogen medium (saturated with water vapour) do not - in and of themselves - tell you much about how hydrogen and helium may form solid bodies in the low-temperature, near vacuum of the ISM, do they?

You are so literal in your interpretations. I'm merely pointing out that the existence of trace amounts of dust promote condensation and giving you an example from common experience. If you don't believe that this can apply in the cosmos, please explain how planets can form containing vast quantities of hydrogen and helium.

A recent paper was already sited about the possibility of frozen hydrogen.

I said:

I'm not aware of any such detection. However since we cannot detect 1km snowballs in the Oort I think it's probably impossible (just now).

This is getting rather silly, isn't it?

We can't detect 1km gold nuggets in the Oort, nor 1km balls of frozen xenon, nor 1km balls of stromatolite DNA, nor ... Perhaps the missing baryonic mass in spiral galaxies (to explain their rotation curves) is in the form of a mixture of these three things?

What is getting rather silly here is your refusal to concede the point that if there were other forms of matter beside stars gas and dust we would not be able to directly detect them. Also you insist that we know everything there is to know about condensed matter even though we cannot detect it if it does exists.

[QUOTE=Nereid;2012822]
A mass of hydrogen and helium, with a teensy amount of metals, can contract under its own gravity, and efficiently get rid of the 'contraction energy' through electromagnetic radiation (that's what the metals do). 'Dust' which clumps to form planetismals can become massive enough to hold hydrogen and helium against escape.
[QUOTE]

Yes, that is partly my point. Do you suppose that no condensation occurred before a Neptune-size mass was gathered and then all at once condensed into Neptune?

The physics of condensation is very complex and not completely understood. What survives in the formation of the solar system is not necessarily indicative of all conditions.

I hope you are not suggesting that metals are required for condensation.

In either case, the minimum mass of a hydrogen/helium dominated object is ~that of Neptune, isn't it? Otherwise the Earth (and Venus and Mars and ...) would be mini-gas giants (a scaled-down version of Jupiter), wouldn't it?

Why Neptune sized? Because it's the smallest we have detected? Because it's the smallest that could form near the sun? Because it is what is left after all the other chunks have been swept up into the largest chunk around and the remaining small pieces are evaporated by the growing star? If Earth etc. had thick gaseous hydrogen atmospheres, they would have been evaporated by the Sun long ago. Even today gaseous hydrogen cannot long remain earth bound.

Doesn't our galaxy - like a great many other spirals - have a flared, or warped, outer disk?

Your point?

BoTs can be very powerful. And they are relatively quick and easy to do.

Yes and they can also be very misleading because they involve ultra-simplified models and assumptions.

For a BoT, you don't need "precise"; you can reverse-engineer it: what would the size (or mass) distribution function have to look like to satisfy, simultaneously, the 'missing mass' (and its distribution) per rotation curves AND have escaped all attempts at detection, to date?

If you do the calculation, I think you may find the required distribution function is rather, um, odd.

Why don't you do that calculation and tell us what you have concluded?

I said:

That's an enormous gap in the mass distribution of condensed matter objects (~10^31).

Your claim is that little or nothing condenses that is between the size of a dust particle and a small star. That's a mass ratio of ~10^31 (conservatively) within which no condensed matter can exist in any significant quantity. Does that help? This is a mass distribution that I do find odd.

Do you have some references to papers on that, which I could read?

I have not yet read many papers that discuss possible formation of sub-stellar objects in general. I did find Pfenniger's work which argues for a fractal density distribution of even gas that leads to serious miscalculation of mass based on HI detection. He also argues that small dense clouds are sufficiently stable to persist and continually form. He is further suggesting that there might be frozen forms of H.

If you want to tell me about some papers that criticize this work, fine.

If you haven't heard that stars have been detected at z~6 or that cold temperatures (~10K) seem to be required, then I think you need to do some reading.

[Nereid]

Go to arvix.org. Type Pfenniger in the Author box, select Physics astro-ph.

Thanks.

Among the 39 I get when I do this, is there any one, or half dozen, you'd particularly recommend?

I'm particularly interested in learning how helium can condense into solids.

Come on Nereid. That's a strawman, nobody said it could.

Perhaps I misunderstood what you wrote. Here's the trail:
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Me: The question, surely, would be whether matter hydrogen and helium can condense into solids even in the presence of radiation. Is there any evidence, of any kind, that they can?

You: Yes, and some theorist (e.g. Daniel Pfenniger) are trying to figure this out.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
So, did you mean to write something like this: "No, there is no such evidence; but some theorists (e.g. Daniel Pfenniger) are trying to figure out how hydrogen can condense into solids even in the presence of radiation (no one has suggested that helium could do this)."

As I understand it, certain bacteria can form nucleation centres for snowflakes too.

However, the mechanisms for the formation of snowflakes in a high-temperature, high density oxygen-nitrogen medium (saturated with water vapour) do not - in and of themselves - tell you much about how hydrogen and helium may form solid bodies in the low-temperature, near vacuum of the ISM, do they?

You are so literal in your interpretations.

Thank you.

I'm merely pointing out that the existence of trace amounts of dust promote condensation and giving you an example from common experience.

And "common experience" is a reasonable basis for speculating about unknown forms of cold, dark, baryonic matter in the outer disks of spiral galaxies?

As if we don't have centuries of hard-won, well-established physics to use instead?

By this kind of logic, would it be reasonable (to you) to say something like "the burning of wood generates heat and light; perhaps the Sun shines because it's a giant, burning wood-pile"?

If you don't believe that this can apply in the cosmos, please explain how planets can form containing vast quantities of hydrogen and helium.

Hmm, clearly you didn't understand the point I was trying to make.

My mistake; let me try again. Imagine this dialogue:

What are the physical processes involved in the formation of snowflakes, in the Earth's atmosphere? Here is a list {insert list here}. Which of those processes require conditions we know do not exist, wrt condensation in the ISM? Well, {list}, which is, as you can see, pretty much the whole list. Or not. The point? ascribing similarity to underlying physical processes, without the slightest hint of checking for applicability, is a bit like saying "here's a soap bubble, notice that it's spherical in shape. Here's a planet, notice that it's also spherical in shape. Clearly we can learn how planets become spherical in shape by studying how soap bubbles become spherical in shape." (in this case, we already know that the underlying physics is completely different).

A recent paper was already sited about the possibility of frozen hydrogen.

[nitpick]I think you meant to say "cited"[/nitpick]

I said:

I'm not aware of any such detection. However since we cannot detect 1km snowballs in the Oort I think it's probably impossible (just now).

What is getting rather silly here is your refusal to concede the point that if there were other forms of matter beside stars gas and dust we would not be able to directly detect them. Also you insist that we know everything there is to know about condensed matter even though we cannot detect it if it does exists.

Not at all.

IIRC, we had someone, a long time ago now, trying to present the case that CDM is iron balls (that's a simplification).

Again, you seem to have missed the key point I was trying to make.

Speculation is fun. And it may lead to interesting ideas which, maybe, might one day become testable, quantitative hypotheses.

Being open minded is good. Being so open-minded that your brains fall out is not.

If you think that there are (non-exotic) forms of baryonic matter which could comprise a significant proportion of the estimated mass needed to account for the observed rotation curves of spiral galaxies, forms which have as yet not been detected, by all means say so (you've done this). However, if you propose that these forms are "1km snowballs", like those "in the Oort", then you're being silly. You yourself have already ruled those kinds of thing out.

A mass of hydrogen and helium, with a teensy amount of metals, can contract under its own gravity, and efficiently get rid of the 'contraction energy' through electromagnetic radiation (that's what the metals do). 'Dust' which clumps to form planetismals can become massive enough to hold hydrogen and helium against escape.

Yes, that is partly my point. Do you suppose that no condensation occurred before a Neptune-size mass was gathered and then all at once condensed into Neptune?

The physics of condensation is very complex and not completely understood. What survives in the formation of the solar system is not necessarily indicative of all conditions.

I hope you are not suggesting that metals are required for condensation.

As I understand it, metals are, indeed, required for gravitationally-bound objects with masses of ~Neptune to ~10 sols to form out of clouds of hydrogen and helium, in the conditions of early universe.

In either case, the minimum mass of a hydrogen/helium dominated object is ~that of Neptune, isn't it? Otherwise the Earth (and Venus and Mars and ...) would be mini-gas giants (a scaled-down version of Jupiter), wouldn't it?

Why Neptune sized? Because it's the smallest we have detected? Because it's the smallest that could form near the sun? Because it is what is left after all the other chunks have been swept up into the largest chunk around and the remaining small pieces are evaporated by the growing star?

Because the gas in the upper atmosphere of gravitationally-bound objects, composed predominantly of H and He, with considerably less mass, will be hot enough for molecules in the high-velocity tail of the Maxwell-Boltzmann to escape, in times much shorter than Hubble time. The temperatures will be that high because of gravitational contraction; the local g will not be great enough to hold the H₂ and He.

If Earth etc. had thick gaseous hydrogen atmospheres, they would have been evaporated by the Sun long ago.

An Earth-sized (mass), gravitationally bound object will lose its hydrogen and helium very early in its life; the Sun certainly helps, but is not necessary. Unless, that is, the H and He is not in the form of H₂ and gaseous He (e.g. chemically bound, as water; trapped in crystals, released in radioactive decay, ...).

Doesn't our galaxy - like a great many other spirals - have a flared, or warped, outer disk?

Your point?

We can see our own galaxy's outer disk (or a large part of the flared, or warped part), because it is seen well away from the galactic plane. Remember, this is what you wrote: "Study of the outer arms of our own galaxy with this method may be very difficult due to dust and the lack of background stars."

(to be continued)

[TooMany]

You really don't know many astronomers, do you? In fact, do you know any?

I mean, how can you possibly know what motivates any astronomer?

If I were to start making wild assumptions about your motivations, then drawing conclusions from those assumptions, you'd scream, loud and clear, wouldn't you*?

Yet you show no qualms about making ridiculous claims about hundreds, if not thousands, of people you have never even met!

Why, oh why, do you do this (if I may ask)?

It's because people are human, not computers, even scientists and astronomers. All you have to do is observe the debate to see such motivations. People become attached to theories and are reluctant to accept contradicting information or they may attempt to rationalize such information. This is a simple fact of human nature. It has been going on throughout the entire history of science.

Astronomers such a Ned Wright go so far as to mock suggestions that CMB anomalies are meaningful by writing a paper that shows Steven Hawkings initials in the CMB. You don't see a motivation behind that I suppose? Perhaps it's unfair and unwise to attribute such motivations more broadly. Perhaps there are many more of those like Pfenniger who are quietly working on ways to explain things in ways that need not be consistent with LCDM.

I will admit my motivations for continuing to argue (up to this point) against this brick wall. I don't particularly like the theory, I find it far from convincing, not because I understand all the math and observations, but because every time a problem comes up another unproved and difficult to falsify assumption is added to keep it alive. At the same time that the existence of non-baryonic matter has not even been demonstrated, it is insisted that there cannot more any more baryonic matter.

Here's another example: we've been over this, and you already at least acknowledged the errors and weaknesses in the presentation of your case. Yet, here we are, mere days later, and you're repeating the same things!

Yes it is getting tedious, as are your denials such as in the last exchange (gold nuggets?). I have done the best I can (at the moment) to point out that there are severe limits to what we actually know about baryonic matter in our own galaxy. Also I have pointed to papers indicating that there are good reasons to expect that much more exists. More baryonic matter helps explains things that are currently puzzles in the context of LCDM.

You will acknowledge no weakness in your arguments. It's all figured out. We know it all. No need to think about baryonic matter, we already know it's not there via our BoT calculations.

Oops, but what about all the problems that have shown up with LCDM. Do you need a list?

I would suggest that if the attitude toward alternative explanations in the astronomical community is reflected by the attitudes expressed in this forum, then things will indeed move forward rather slowly. But admittedly if you look at history, this is what often happens in science.

Poor Pfenniger, I have to admire his persistence, patience, willingness to compromise to make a point and to try to get others to think about possibilities outside the bounds of a theoretical straight jacket.

Instead of telling me that I don't know anything (as an explanation of why there cannot be more baryonic matter than we can detect), why don't you refer to some papers that make your point.

[TooMany]

Nereid, I've much appreciated your input and reference to papers. I am however tired of your nitpicking everything I say and twisting it into something I did not in order to discredit my whole point:

We can see our own galaxy's outer disk (or a large part of the flared, or warped part), because it is seen well away from the galactic plane. Remember, this is what you wrote: "Study of the outer arms of our own galaxy with this method may be very difficult due to dust and the lack of background stars."

The detection of a warp in our galaxy has nothing to do with what we can discern concerning the state of baryonic matter at small scales in the outer arms using the method of micro lensing, which is what my statement was in reference to. Your attempt to discredit my statement in this way is either extremely naive or disingenuous.

If you have something enlightening to add fine, but I'm done with your obstinate battle to defend against any possibility of additional baryonic matter in this manner. It is unproductive as is basing arguments on the existence of Neptune and nothing similar that is smaller in the solar system.

[StupendousMan]

Instead of telling me that I don't know anything (as an explanation of why there cannot be more baryonic matter than we can detect), why don't you refer to some papers that make your point.

http://arxiv.org/abs/0712.1100

[TooMany]

http://arxiv.org/abs/0712.1100

They compare their observations of lithium and iron to models of stellar diffusion, finding evidence that both lithium and iron have settled out of the
atmospheres of these old stars. Applying their stellar models to the data they infer for the unevolved abundances, [Fe/H] = –2.1 and [Li] = 2.54 ± 0.10, in excellent agreement with the SBBN prediction. More such data are eagerly anticipated.

Presto! Lithium problem solved! Oops, now we don't know how much iron (many times denser than lithium) is in any star, including the ones made of "primordial matter". More such data are eagerly anticipated. Indeed.

[TooMany]

Interestingly, this must be the same Mark Walker who publicised the Extreme Scattering Events. Although the article doesn't connect the topics, I can only think that Walker is quietly positing frozen hydrogen as the source of the scattering clouds.

Extreme scattering events and Galactic dark matter

http://arxiv.org/abs/astro-ph/9802111

Your right. I didn't notice that but I have read the paper you refer to. There don't seem to be many astronomers pursuing these things (proof that it's nonsense).

[Squink]

People become attached to theories and are reluctant to accept contradicting information or they may attempt to rationalize such information. This is a simple fact of human nature. It has been going on throughout the entire history of science.

Back in 1974, the textbooks told us that statistical analysis of galaxy distribution fueled a consensus among astronomers that superclusters do not exist. A closed universe perfectly poised to undergo endless cycles of expansion and contraction ruled the cosmological pantheon (see Smith & Jacobs "Introductory Astronomy and Astrophysics", 1973). Despite your 'reluctance' factor, and to the credit of scientists, who also happen to be people, cosmology has moved forward substantially since that ancient time. It's been a data driven advance, rather than a personality driven advance. The concensus changes in response to new information. AFAIK, that mode of operation hasn't changed among the new generation of cosmologists.

[TooMany]

Back in 1974, the textbooks told us that statistical analysis of galaxy distribution fueled a consensus among astronomers that superclusters do not exist. A closed universe perfectly poised to undergo endless cycles of expansion and contraction ruled the cosmological pantheon (see Smith & Jacobs "Introductory Astronomy and Astrophysics", 1973). Despite your 'reluctance' factor, and to the credit of scientists, who also happen to be people, cosmology has moved forward substantially since that ancient time. It's been a data driven advance, rather than a personality driven advance. The concensus changes in response to new information. AFAIK, that mode of operation hasn't changed among the new generation of cosmologists.

I agree with that and it's quite possible for the whole theory to change again like it did 1974. I'm not dumping on scientist like some GW denier. I'm reacting to two things. One is the tendency to rationalize to retain theories in the face of problems. The other is worse, like the discussion with Nereid which I take as his avoidance of serious consideration of alternatives in order to preserve the status quo. When you start making silly remarks about "gold nuggets", using Neptune to argue that all condensates must be that size and distorting what people assert in order to defend your point, it is not entirely healthy.

Interesting problems are arising. Insisting that we already know all there is to know about something does not help solve them. Observation is the ultimate decider and we all have to bow to it. I eagerly await any and all new information.

[Nereid]

It's because people are human, not computers, even scientists and astronomers. All you have to do is observe the debate to see such motivations. People become attached to theories and are reluctant to accept contradicting information or they may attempt to rationalize such information. This is a simple fact of human nature. It has been going on throughout the entire history of science.

Astronomers such a Ned Wright go so far as to mock suggestions that CMB anomalies are meaningful by writing a paper that shows Steven Hawkings initials in the CMB. You don't see a motivation behind that I suppose? Perhaps it's unfair and unwise to attribute such motivations more broadly. Perhaps there are many more of those like Pfenniger who are quietly working on ways to explain things in ways that need not be consistent with LCDM.

I will admit my motivations for continuing to argue (up to this point) against this brick wall. I don't particularly like the theory, I find it far from convincing, not because I understand all the math and observations, but because every time a problem comes up another unproved and difficult to falsify assumption is added to keep it alive. At the same time that the existence of non-baryonic matter has not even been demonstrated, it is insisted that there cannot more any more baryonic matter.



Yes it is getting tedious, as are your denials such as in the last exchange (gold nuggets?). I have done the best I can (at the moment) to point out that there are severe limits to what we actually know about baryonic matter in our own galaxy. Also I have pointed to papers indicating that there are good reasons to expect that much more exists. More baryonic matter helps explains things that are currently puzzles in the context of LCDM.

You will acknowledge no weakness in your arguments. It's all figured out. We know it all. No need to think about baryonic matter, we already know it's not there via our BoT calculations.

Oops, but what about all the problems that have shown up with LCDM. Do you need a list?

I would suggest that if the attitude toward alternative explanations in the astronomical community is reflected by the attitudes expressed in this forum, then things will indeed move forward rather slowly. But admittedly if you look at history, this is what often happens in science.

Poor Pfenniger, I have to admire his persistence, patience, willingness to compromise to make a point and to try to get others to think about possibilities outside the bounds of a theoretical straight jacket.

Instead of telling me that I don't know anything (as an explanation of why there cannot be more baryonic matter than we can detect), why don't you refer to some papers that make your point.

I had a nice, long, response prepared ... and it disappeared.

Key point: where can we start a science-based discussion, on extra-galactic astrophysics, TooMany?

Is it OK to assume the Standard Model (of particle physics)? General Relativity? If not, what?

[Nereid]

One is the tendency to rationalize to retain theories in the face of problems.

Funny thing that.

Imre Lakatos pointed that out too.

Many decades ago.

As you would know if you'd gone to a library.

And why are such things retained, in the face of apparently contradictory evidence? Might it be, perhaps, because there's no better alternative?

The other is worse, like the discussion with Nereid which I take as his avoidance of serious consideration of alternatives in order to preserve the status quo.

I get that. Really I do. I might even go so far as to say I see, in your posts, a reflection of much younger me.

Did you stop to think what I might see? That your use of "his" is a give-away (in light of an earlier post of mine)? That you have shown essentially no evidence - of an objective kind - that you actually understand most key aspects of the topic you are so passionate about? That your posts reflect an, um, poor ability to think critically?

When you start making silly remarks about "gold nuggets", using Neptune to argue that all condensates must be that size and distorting what people assert in order to defend your point, it is not entirely healthy.

Yeah, it's awful, isn't it?

Like continuing to argue a case you've already accepted is dead (and have said so, explicitly).

Interesting problems are arising.

Yes, they are.

Insisting that we already know all there is to know about something does not help solve them.

Yes, that's terrible, isn't it?

How fortunate, then, that no one in this thread has insisted anything of the sort.

Observation is the ultimate decider and we all have to bow to it. I eagerly await any and all new information.

Good.

In the meantime, why not spend some time in the library? Learning about this interesting topic?

[Nereid]

Nereid, I've much appreciated your input and reference to papers. I am however tired of your nitpicking everything I say and twisting it into something I did not in order to discredit my whole point:

We can see our own galaxy's outer disk (or a large part of the flared, or warped part), because it is seen well away from the galactic plane. Remember, this is what you wrote: "Study of the outer arms of our own galaxy with this method may be very difficult due to dust and the lack of background stars."

The detection of a warp in our galaxy has nothing to do with what we can discern concerning the state of baryonic matter at small scales in the outer arms using the method of micro lensing, which is what my statement was in reference to. Your attempt to discredit my statement in this way is either extremely naive or disingenuous.

Fair enough, apologies for misunderstanding your intent.

But ... why did you write "may be very difficult due to dust"?

And why do you (apparently) think there is a "lack of background stars" in directions above the galactic plane (and away from the Magellanic Clouds)?

I'm genuinely interested, because, as far as I know, dust is not a problem (with doing microlensing studies above the galactic plane, say |b|>10^o), and the number of background stars needed to do such studies is not at all intuitively obvious, especially when you consider what Pan-STARRS and the LSST should be capable of.

If you have something enlightening to add fine, but I'm done with your obstinate battle to defend against any possibility of additional baryonic matter in this manner.

I wasn't aware that that's what I was doing.

I thought I was trying to get you to think more deeply, to go to a library, to research the topic you are so (apparently) passionate about, etc.

It is unproductive as is basing arguments on the existence of Neptune and nothing similar that is smaller in the solar system.

Is that what I did?

Well, if you think so, then I have clearly failed, in terms of communication.

Oh, and what do you think astrophysics - or science in general - is, if not disciplined, systematic nitpicking?

[slang]

Well, if you think so, then I have clearly failed, in terms of communication.

Not to everyone, to be sure.

[TooMany]

Nereid, this is going nowhere. You are attempting to distort something here:

And why do you (apparently) think there is a "lack of background stars" in directions above the galactic plane (and away from the Magellanic Clouds)?

Because I was not talking about above. Because in comparison with the number of stars available toward the MCs and the galactic center, they are quite sparse indeed in the plane. Because micro lensing is rare event, it makes any conclusion difficult with a low density of background stars.

I'm genuinely interested, because, as far as I know, dust is not a problem (with doing microlensing studies above the galactic plane, say |b|>10o), and the number of background stars needed to do such studies is not at all intuitively obvious, especially when you consider what Pan-STARRS and the LSST should be

Because dust does obscure much of the outer parts of our galaxy. We were taking about the galactic plane in discussing the outer arms. Not 10 degrees above and certainly not at the MC angles.

I've had quite enough of these useless responses. You know full well I'm pointing out valid difficulties in using this technique to find even Jupiter-sized bodies in the outer disk. And if you are not aware of these issues, then it is you who needs a trip to the library.

You wish to contradict everything I say with some distortion of what we are talking about. It is a fruitless game. Tah tah.

[Cougar]

I'm reacting to two things. One is the tendency to rationalize to retain theories in the face of problems.

You appear to be reading too much Halton Arp or Peter Woit. You have a skewed understanding of scientists. What I would watch out for is the tendency to reject any and all mainstream positions before even understanding those mainstream positions fully, using quote-mining techniques, and responding with arguments that make no sense and just deflect the issue, as in the following example:

http://arxiv.org/abs/0712.1100
Presto! Lithium problem solved! Oops, now we don't know how much iron (many times denser than lithium) is in any star, including the ones made of "primordial matter".

The amount of iron "in any star" is not an issue. The amount of lithium in the early universe is a tracer of exactly how the first three minutes of the Universe went down. This is of interest.

[Cougar]

"When the temperature dropped far below one billion degrees [three minutes after the big bang] this 'primordial nucleosynthesis' stopped and, according to the standard model, we should be left with roughly 25% helium by mass and 2 x 10^-5 parts deuterium. It may seem like a miracle that astronomers in fact do measure about 25% helium in the real universe, but it is a miracle squared that they also measure something like 2 x 10^-5 parts deuterium." -- Tony Rothman

[antoniseb]

Head Up!

Local Dark Matter...

http://arxiv.org/abs/1205.4033 ... I haven't read this paper yet, but the abstract says that it is a reply to the paper referenced in the OP of this thread. More discussion later. Also, this paper will be in my list for "Fun Papers" tonight/tomorrow.

[kzb]

Head Up!

Local Dark Matter...

http://arxiv.org/abs/1205.4033 ... I haven't read this paper yet, but the abstract says that it is a reply to the paper referenced in the OP of this thread. More discussion later. Also, this paper will be in my list for "Fun Papers" tonight/tomorrow.

Wow that was quick ! Round 2 to Bovy et al, hopefully there'll be a Round 3...you would expect Moni Bidin to at leat respond to this.

I've not read in detail yet either, but was not the fatal problem identified here, i.e. the assumption of a constant circular velocity with z, not discussed in the first paper ? And the affect of this on the conclusions? I'll have to go back and check that now.

[antoniseb]

Wow that was quick ! Round 2 to Bovy et al, hopefully there'll be a Round 3...you would expect Moni Bidin to at leat respond to this.

I've not read in detail yet either, but was not the fatal problem identified here, i.e. the assumption of a constant circular velocity with z, not discussed in the first paper ? And the affect of this on the conclusions? I'll have to go back and check that now.

I'm still looking it over, but as I mention in the Fun Papers note about it, the result from the idea in the first paper, and the reworked math in the second paper is the most precise determination of the distribution of DM in our galaxy so far. The conclusion of the first paper may have been way off from a flaw in their math, but the idea is a useful one.

[Cougar]

Go to arvix.org. Type Pfenniger in the Author box, select Physics astro-ph.

You mean arxiv? This yields 39 papers. Are we supposed to review them all to determine which one(s) you're talking about?

By the way, Pfenniger himself points out:

"...we do not forget that excellent arguments exist also to expect substantial amounts of hot intergalactic gas, as well as dominant non-baryonic dark matter(s) at cosmological scales."

[TooMany]

Head Up!

Local Dark Matter...

http://arxiv.org/abs/1205.4033 ... I haven't read this paper yet, but the abstract says that it is a reply to the paper referenced in the OP of this thread. More discussion later. Also, this paper will be in my list for "Fun Papers" tonight/tomorrow.

Isn't astronomy wonderful! Name a paper and you can find one that contradicts it. This analysis will be correct for believers in CDM and vice versa.

Indicates that one should take with a grain of salt, both sides of the issue. Haven't read it yet either; it will probably be over my head. It will be interesting to see how the other authors respond though. Perhaps they will admit a mistake, perhaps not?

[antoniseb]

Isn't astronomy wonderful! Name a paper and you can find one that contradicts it. This analysis will be correct for believers in CDM and vice versa. ...

This isn't like political news reporting. In this particular case, one side will be right, and the other will be wrong. It is not up to popular choice. One really important thing the first paper did was show that there is a mechanism that plausibly can be used to find local dark matter densities in the galaxy. The second paper pointed out an error made in the first paper, but the technique more broadly is an advance for all of astronomy (a win-win).

[Cougar]

Indicates that one should take with a grain of salt...

This is pretty much true for any single paper recently published. A single paper does not firmly establish a particular idea or finding. Obviously the more papers confirming a finding, the more well established that finding becomes.

As an example in contrast, there were two independent papers released at the same time presenting independent data that indicated the expansion was accelerating. This gave the finding a lot more credibility, and, though floored, most astronomers "leaped from the carpet, dusted themselves off, and proceeded to investigate the universe" (as Donald Goldsmith described it).

[TooMany]

You mean arxiv? This yields 39 papers. Are we supposed to review them all to determine which one(s) you're talking about?

You only need to read the titles to pick some out. About a third of them directly refer to baryonic dark matter or condensed hydrogen or high velocity clouds.

By the way, Pfenniger himself points out:

"...we do not forget that excellent arguments exist also to expect substantial amounts of hot intergalactic gas, as well as dominant non-baryonic dark matter(s) at cosmological scales."

Correct and that excellent argument for CDM is the BBT itself and the analysis of the CMB that supports the theory. My preference is to put a little more emphasis on what we can find by looking nearby rather than trying to determine the composition and structure of galaxies by reading tea leaves in the farthest, coldest reaches of space and speculating about the first seconds of creation. Let's come back to the Local Group and the Galaxy and figure out what's really going on with them. The mainstream in astronomy is currently driven by conclusions from the CMB. Well, there comes a time when you must back up those conclusions with observations of the here and now.

Hard evidence for the existence of CDM is completely lacking. Where are the WIMPs in particle physics? Contradictions are many in the local universe. Galaxies (e.g. tidal dwarfs) without CDM behave just like galaxies with it. What's with that? Where are the predicted hundreds of randomly distributed dwarf galaxies around the Galaxy? Where are the CDM cusps? Where is the rest of the baryonic matter? How can the bottom up merger model explain the formation of the beautiful spiral galaxies that dominate the population?

If you would like an extensive list of issues with current theory, I recommend this recent paper by Pavel Kroupa: The dark matter crisis: falsification of the current standard model of cosmology. In the paper he builds a very a detailed case against CDM. He includes a nice summary of the new physics postulated to support LCDM over the years and the motivations. There is also a broader list of issues with LCDM theory.

I'm really looking forward to the next decade of discovery. Perhaps if we put the CMB in the backseat for a while we can get somewhere. Right now our wheels seem to be spinning trying to account for conflicts with the CMB. It's even possible that the basic assumptions of BBT are completely wrong, even though consistent with many findings. After all, Earth-centered cosmology stood for many centuries, even with the application of mathematics. In a presentation Kroupa points out that the proposal that the sun was a center for the planets and that the Earth was a separate center for the moon was deemed to complicate an already elegant and well-established Earth-centered theory, that is until Galileo discovered the moons of Jupiter.

[Cougar]

...reading tea leaves in the farthest, coldest reaches of space and speculating about the first seconds...

This is extremely insulting to the scientists who have produced and continue to produce very solid research on the CMB and the first three minutes. If you have no understanding of this research, which appears to be the case, you really should not be so denigrating. Such research is about as far from "reading tea leaves" and idle speculation as you can get.

[Cougar]

If you would like an extensive list of issues with current theory, I recommend this recent paper by Pavel Kroupa: The dark matter crisis: falsification of the current standard model of cosmology.

Ah, a Milgromian. Good luck with that.

[TooMany]

This isn't like political news reporting. In this particular case, one side will be right, and the other will be wrong. It is not up to popular choice. One really important thing the first paper did was show that there is a mechanism that plausibly can be used to find local dark matter densities in the galaxy. The second paper pointed out an error made in the first paper, but the technique more broadly is an advance for all of astronomy (a win-win).

I wonder if these guys ever talk to each other before they fire off a paper contradicting each other's findings?

No, no, no, I don't think it's anything like politics! Politics is just pure ** that services a hidden agenda. I really just meant that the data is ambiguous in many ways. It's very complicated to sort out. Unlike lab experiments there are no conditions that can be deliberately held constant. Thus a predisposition for a certain result could lead a non-android to overlook or underestimate/overestimate something.

Perhaps the original authors will admit an error, we will see. The essence of the counter-argument seems to be this:

We demonstrate that the assumption of constant mean azimuthal velocity is physically implausible by showing that it requires the circular velocity to drop more
steeply than allowed by any plausible mass model, with or without dark matter.

Then they assume that circular velocity is constant instead, but I'm not sure they prove that. There may be other hidden assumptions in there that I don't understand (in both papers). By "circular velocity" are they referring to the tangential velocity relative to the galactic axis or relative to the center of galactic mass? What exactly is the "azimulthal velocity", is that tangential relative to the axis? I got a little lost in all the vectors, let alone the equations.

I certainly agree that the idea is a win for analyzing density. This is the kind of science I like to see. I cannot find it in myself to draw hard conclusions about galaxies from the CMB and calculations about the unobserved dawn of creation.

[TooMany]

Ah, a Milgromian. Good luck with that.

Ah, let the name be the judge of the science, for we need only identify those who are the sayers of the truth to safely condemn the others.
No purpose in exposing one's eyes to those wicked words since they are tainted from the start.

Good luck with that.

[TooMany]

This is extremely insulting to the scientists who have produced and continue to produce very solid research on the CMB and the first three minutes. If you have no understanding of this research, which appears to be the case, you really should not be so denigrating. Such research is about as far from "reading tea leaves" and idle speculation as you can get.

The insult is in your mind. It is just a bit of hyperbole (see rhetorical devices) to describe an explanation of galaxy dynamics based on some tiny, random-looking variations in the coldness of deep space. I.e. scientist are employing some very indirect evidence (which itself requires an assumption of some new physics along the way) to propose yet more new physics. I am certainly not implying that the CMB analysis was done without the hard work of many very smart people. Neither can I prove that their analysis is wrong, but I'm having some serious doubts.

[parejkoj]

I certainly agree that the idea is a win for analyzing density. This is the kind of science I like to see. I cannot find it in myself to draw hard conclusions about galaxies from the CMB and calculations about the unobserved dawn of creation.

You know, its funny. I'm not entirely sure you're willing to draw quantitative conclusions about anything whatsoever. Perhaps you'd like to give my BAUT Supernova Challenge a try, and include the predictions of your favorite cosmologies? After-all, you gave the original impetus for my idea...

As to your list of potential problems with CDM, I already gave you some possible solutions to some of them (in one of these threads), and a list of [citation needed] for others. Also, "beautiful spiral galaxies" certainly don't "dominate the population" of galaxies.