Questions regarding dark matter dynamics

In summary, there is astronomical evidence that dark matter has different densities in different parts of the observable universe. This is supported by the relationship between the middle radius and average orbital velocity of stars in galaxies, as well as observations of hydrogen ions and gravitational lensing. Recent studies have shown that the amount of dark matter in early galaxies does not exceed the amount of luminous matter, which raises questions about the existence of extra-galactic dark matter. However, it is important to note that this does not necessarily mean that dark matter does not exist, as its formation and evolution are still not well understood.
  • #1
Buzz Bloom
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I recall reading somewhere (I can't remember where) that there is astronomical evidence that dark matter has different densities in different parts of the relatively near parts of the observable universe.
Q1. Is this correct? If so, can someone please post a link to a relevant article?

The following observational possibility come to mind.
Consider the relationship R(r,v) between (1) the middle radius r of a cylindrical shell centered on the center of gravity a galaxy, and parallel to the axis of the total angular momentum of the stars in the galaxy, and (2) the average orbital velocity v of stars observed within that cylindrical shell. I understand that observers have noticed that this relationship R(r,v) is very much dissimilar from what would be expected if dark matter was not present.
Q2. Can the density ρDM of a dark matter "cloud" surrounding a galaxy be estimated by the galaxy's relationship R(r,v)? Does anyone know whether this has been done? If "yes", does anyone know if the variability of such estimates show statistically significant differences (based on the observational error range of the individual ρDM estimates) between the individual values and their average?

Q3. The same question as Q2 except applied to galaxy clusters and their galaxies, rather than galaxies and their stars.

Any responding posts will be much appreciated, especially those with links to relevant articles.
 
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  • #2
I thought they were measuring hydrogen ions. Emission frequency gets red shifted which tells us the ion's velocity. The interstellar gas that is orbiting far away from galaxy centers moving too fast relative to stars and ions in the galaxy center. This is the original reason to believe that dark matter exists. There has to either be mass we cannot see or our model of gravity is wrong.

Here is a paper from 1966:
http://adsabs.harvard.edu/doi/10.1086/153889
And from 1978:
http://ned.ipac.caltech.edu/level5/March05/Bosma/frames.html

I found them on wikipedia's references.

The recent work on dark matter using gravitational lensing is not very local.
 
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  • #3
I agree.

There is a general consensus that Einstein rings show a large mass discrepancy between luminous and non-luminous mass compatible with the missing mass of dark matter. Looking at some recent papers, Magain, P. and Chantry, V. (2013) and Yong Tian1 and Chung-Ming Ko (2017) there appears only about as much missing mass as there is luminous mass. In the latter paper the researchers plot Mob / Mbar versus gbar (acceleration due to gravity from the baryonic mass), where Mob is the observed mass from the Einstein ring and Mbar is the baryonic (luminous) mass which gives an almost flat line between 1 and 2. Since Mob = Mbar + Mdm, Mob / Mbar = 1 + Mdm / Mbar: then if Mob / Mbar = 1, then Mdm = 0; and if Mob / Mbar = 2, then Mdm = Mbar. The conclusion is that the range of Mdm is; 0 < Mdm < Mbar. The first paper concludes: ‘Our results thus suggest that, if dark matter is present in early-type galaxies, its amount does not exceed the amount of luminous matter and its density follows that of luminous matter, in sharp contrast to what is found from rotation curves of spiral galaxies.’

These two papers are in complete agreement. Similar conclusions were reached by McGaugh et at (2016) and Lelli (2016). This seriously questions the idea of extra-galactic dark matter of any density.
 
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  • #4
Adrian59 said:
I agree.

There is a general consensus that Einstein rings show a large mass discrepancy between luminous and non-luminous mass compatible with the missing mass of dark matter. Looking at some recent papers, Magain, P. and Chantry, V. (2013) and Yong Tian1 and Chung-Ming Ko (2017) there appears only about as much missing mass as there is luminous mass. In the latter paper the researchers plot Mob / Mbar versus gbar (acceleration due to gravity from the baryonic mass), where Mob is the observed mass from the Einstein ring and Mbar is the baryonic (luminous) mass which gives an almost flat line between 1 and 2. Since Mob = Mbar + Mdm, Mob / Mbar = 1 + Mdm / Mbar: then if Mob / Mbar = 1, then Mdm = 0; and if Mob / Mbar = 2, then Mdm = Mbar. The conclusion is that the range of Mdm is; 0 < Mdm < Mbar. The first paper concludes: ‘Our results thus suggest that, if dark matter is present in early-type galaxies, its amount does not exceed the amount of luminous matter and its density follows that of luminous matter, in sharp contrast to what is found from rotation curves of spiral galaxies.’

These two papers are in complete agreement. Similar conclusions were reached by McGaugh et at (2016) and Lelli (2016). This seriously questions the idea of extra-galactic dark matter of any density.

The conclusion that dark matter is not present in early galaxies is not the same as concluding that dark matter does not exist. The early galaxies are also missing iron for example.
 
  • #5
I would suggest that the formation of iron from precursor nuclei is well established. The same is not apparent for dark matter. Even if dark matter evolves from one type of dark matter particle to another there would have to be some form of dark matter in an early galaxy unless baryonic matter can transform to dark matter! Alternatively, the dark matter can coalesce around the galaxy later but I thought one of the drivers for dark matter was seeding of galaxies so one would think it would be there already at galaxy formation.
 
  • #6
stefan r said:
The conclusion that dark matter is not present in early galaxies is not the same as concluding that dark matter does not exist.
Adrian59 said:
I would suggest that the formation of iron from precursor nuclei is well established. The same is not apparent for dark matter.
Hi stefen and Adrian:

There is strong evidence that the amount of non-baryonic (dark) matter is about five times as much as baryonic (ordinary) matter, and this ratio has been stable since the time of primordial nucleosynthesis which took place between about ten seconds and twenty minutes after the big bang.
The discovery that only about 1/6 of matter was baryonic was known before the dark matter influence on star velocities within a galaxy was discovered. The following 1999 paper discusses the discovery based on Deuterium abundances, but I think this idea was around much earlier.

Regards,
Buzz
 
  • #7
I thought nucleosynthesis was about the production of nuclei from baryons, so I can't see how this has any relation to dark matter. The second paper you gave a link to is quite old (1996) and comments that 40% dark matter is in 'compact nucleonic objects'. Now these would be labelled as MACHOs but the current standard model is that dark matter is non-baryonic.
 
  • #8
Adrian59 said:
I thought nucleosynthesis was about the production of nuclei from baryons, so I can't see how this has any relation to dark matter.
Hi Adrian:
It is known what the density of matter is (to reasonable precision), and also what it was was during nucleosynthesis. The reasoning that a large fraction was not protons and neutrons at the time is that if it had been, then the amount of deuterium that would have been made and not consumed in the making of helium would be different than the observed deuterium density.

Regarding the wrong guesses during the 1990's about what dark matter might be made of, scientists of several persuasions are still making wrong guesses, so that hasn't changed much.

Regards,
Buzz
 
  • #9
Buzz Bloom said:
I recall reading somewhere (I can't remember where) that there is astronomical evidence that dark matter has different densities in different parts of the relatively near parts of the observable universe.
Q1. Is this correct? If so, can someone please post a link to a relevant article?

The following observational possibility come to mind.
Consider the relationship R(r,v) between (1) the middle radius r of a cylindrical shell centered on the center of gravity a galaxy, and parallel to the axis of the total angular momentum of the stars in the galaxy, and (2) the average orbital velocity v of stars observed within that cylindrical shell. I understand that observers have noticed that this relationship R(r,v) is very much dissimilar from what would be expected if dark matter was not present.
Q2. Can the density ρDM of a dark matter "cloud" surrounding a galaxy be estimated by the galaxy's relationship R(r,v)? Does anyone know whether this has been done? If "yes", does anyone know if the variability of such estimates show statistically significant differences (based on the observational error range of the individual ρDM estimates) between the individual values and their average?

Q3. The same question as Q2 except applied to galaxy clusters and their galaxies, rather than galaxies and their stars.

Any responding posts will be much appreciated, especially those with links to relevant articles.

I think it's important to be extremely cautious about claiming to hold knowledge about the existence of exotic forms of matter based on astronomical studies rather than actual lab results in controlled experimentation. The existence of "dark matter" is strongly based upon the validity of the "estimates" of baryonic mass that we've been using. I can think of at *least* 5-6 different flaws in the baryonic mass estimates that were used in the famous Bullet Cluster study of 2006. The recent revelations of two different types of 'halos' of both million degree plasma, and of hydrogen gas surrounding our own galaxy might also go a long way to explaining galaxy rotation patterns that we observe.

About all you can tell from the lensing data specifically is that there's a serious discrepancy between our baryonic mass estimates techniques based upon light, and our mass estimates based on lensing. The revelations of the last decade would suggest that the lensing data is probably accurate, whereas the baryonic mass estimate techniques of galaxies that we've been using are considerably inaccurate:

The existence of exotic forms of matter are dependent upon the *assumption* that the baryonic galaxy mass estimation techniques were accurate in 2006, and therefore any "missing mass' was necessarily found in a *non baryonic* form of matter.

https://en.wikipedia.org/wiki/Bullet_Cluster

Since 2006 however, there have been five major revelations of a systematic problem with our flawed calculation of stellar masses that are present in various galaxies and galaxy clusters:

1) Two years later in 2008, we "discovered" that we've been underestimating the amount of scattering taking place in the IGM, and the universe is actually at least *twice as bright* as *assumed*, leading to an *underestimation* of stellar mass:

http://www.st-andrews.ac.uk/news/archive/2008/title,21439,en.php

Keep in mind that the entire basis for the baryonic mass calculation of stellar masses relates back to galaxy brightness. They underestimated the brightness aspect by a factor of two in that 2006 lensing study.

2) We also "discovered" a year later that we've been using a *flawed* method of 'guestimating" the number of smaller stars that cannot be directly observed at a distance, compared to the larger mass stars that we actually can observe at a distance. We underestimated stellar counts of stars the size of our sun by a factor of 4. and all of it was quite ordinary baryonic material.

http://www.nasa.gov/mission_pages/galex/galex20090819.html

3) The following year in 2010, we 'discovered" that we've been underestimating the most *common* sized star (dwarf stars) in various galaxies by a *whopping* factor of between 3 and 20 depending on the galaxy type. Again, we grossly underestimated the *normal baryonic material* that is present in galaxies.

http://www.foxnews.com/scitech/2010/12/01/scientists-sextillion-stars/

4) Two years after that, in 2012, we 'discovered' more ordinary baryonic matter *surrounding* every galaxy that exist inside of the stars themselves. In fact they discovered more ordinary baryonic matter in 2012 than had been ''discovered' since the dawn of human history.

http://chandra.harvard.edu/blog/node/398

5) In 2014 we also "discovered" that we have underestimated the number of stars *between galaxies*, particularly galaxies undergoing a collision process like that Bullet Cluster study:

http://www.realclearscience.com/journal_club/2014/11/06/up_to_half_of_stars_may_be_outside_galaxies_108929.html

There's been at least *five* revelations of *serious* baryonic mass underestimation problems used in that 2006 lensing study that claimed to find 'proof' of exotic forms of matter, and all of those error are *in addition to* the missing baryon problem that was resolved recently when we found that our galaxy is embedded in a halo of neutral hydrogen gas.

https://cosmosmagazine.com/space/galaxy-s-hydrogen-halo-hides-missing-mass

There is far more evidence to suggest that the baryonic mass estimates which were used in that Bullet Cluster lensing study were flawed than there is evidence to suggest that any of the "missing mass" was necessarily related to 'exotic' forms of matter. The lab results over the past 10 years would also tend to support that interpretation, including the most recent results from Xenon-1T.

http://www.spacedaily.com/reports/First_Result_from_XENON1T_Dark_Matter_Detector_999.html
 
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  • #10
I randomly picked one:

MichaelMo said:
4) Two years after that, in 2012, we 'discovered' more ordinary baryonic matter *surrounding* every galaxy that exist inside of the stars themselves. In fact they discovered more ordinary baryonic matter in 2012 than had been ''discovered' since the dawn of human history.

http://chandra.harvard.edu/blog/node/398

that's absolutely NOT what the paper itself says. It says (https://arxiv.org/pdf/1205.5037.pdf abstract):

... The mass content of this phase is over ten billion solar masses, many times more than that in cooler gas phases and comparable to the total baryonic mass in the disk of the Galaxy. ...

"Comparable" here means ~2% since Milky Way mass is variously estimated to be 500-800 billion solar masses.
 
  • #11
MichaelMo said:
The existence of "dark matter" is strongly based upon the validity of the "estimates" of baryonic mass that we've been using.
Hi Michael:

I much appreciate your post and all of the links to evidence about underestimating the amount of baryonic matter.

I hope you will comment on the following.
Buzz Bloom said:
The following 1999 paper discusses the discovery based on Deuterium abundances, but I think this idea was around much earlier.
https://arxiv.org/pdf/astro-ph/9611232.pdf
I confess this article is a bit more technical than I can feel comfortable that I have understood it. What I think I understand from this (especially section 2.2 starting on page 7) and other readings from the past I can't site from memory, is that the amount of Deuterium in the observable part of our universe gives us eveidence that a large fraction of matter cannot be baryonic.

Regards,
Buzz
 
  • #12
MichaelMo said:
...

Errors in observed mass can work both ways. Suppose the center of galaxies have more mass than we thought. That makes the rotational velocity more deviant. You would need even more dark matter to explain it.
 
  • #13
nikkkom said:
I randomly picked one:

that's absolutely NOT what the paper itself says. It says (https://arxiv.org/pdf/1205.5037.pdf abstract):

"Comparable" here means ~2% since Milky Way mass is variously estimated to be 500-800 billion solar masses.

I'm pretty sure that both the article and paper are discussing the comparison to the *known baryonic* (stellar) component of the galaxy, and not the virial mass *including* dark matter, but I may have been a bit overzealous with my use of the term "more". It's still a huge amount of mass compared to the known baryonic mass that's been identified to date. Note we've also discovered a whole host of new satellite galaxies around our galaxy since 2006.

Page 7-8:

The mass probed by this warm-hot gas is larger that that in any other phase of the CGM and is comparable to the entire baryonic mass of the Galactic disk ∼ 6 × 10^10M⊙ (Sommer-Larsen 2006). The baryonic fraction fb of this warm-hot gas varies from 0.09−0.23 depending on the estimates of the virial mass of the Milky Way, from 1012M⊙ to 2.5×1012M⊙ ((Anderson & Bregman 2010) and references therein), bracketing the Universal value of fb = 0.17. The oxygen mass in the CGM as traced by O vii /O viii is:

Moxygen = (6.8 ± 5.9) × 108(0.5 fOV II)M⊙ (4)

and with the effective oxygen yield ∼ 0.01 for a Salpeter IMF, the stellar mass needed to produce this amount of oxygen is M⋆ = (6.8±5.9)×10^10M⊙, which is of the order of the disk+bulge stars.

Keep in mind however that this mass is *in addition to* all the other 5 papers relate to galaxy mass estimation problems that were used in 2006.
 
  • #14
stefan r said:
Errors in observed mass can work both ways. Suppose the center of galaxies have more mass than we thought. That makes the rotational velocity more deviant. You would need even more dark matter to explain it.

You're right that the density and the mass layout of the halo makes a difference with respect to galaxy rotation patterns, although it all matters in lensing studies. I would be inclined to believe that the plasma mass would be concentrated closer to the core, and would thin out with distance from the core as "dark matter" halo models predict. The same is true of the mass layout of the non-ionized hydrogen halo, or at least I would presume so.
 
  • #15
Buzz Bloom said:
Hi Michael:

I much appreciate your post and all of the links to evidence about underestimating the amount of baryonic matter.

I hope you will comment on the following.

I confess this article is a bit more technical than I can feel comfortable that I have understood it. What I think I understand from this (especially section 2.2 starting on page 7) and other readings from the past I can't site from memory, is that the amount of Deuterium in the observable part of our universe gives us eveidence that a large fraction of matter cannot be baryonic.

Regards,
Buzz

I'll try to read through that paper this evening and I'll comment more once I've read it, but...

I'm frankly a little apprehensive about "assuming" the existence of exotic forms of matter only to make sure that LCDM mathematically "fits' some other completely different observation. I'd probably feel differently were it not for all the negative results from the various dark matter "tests" at LHC, LUX, PandaX, Xenon100,and even recent Xenon-1T results. As it stands, the nucleosynthesis argument seems more like a case of special pleading, only so that LCDM can be considered exempt by falsification by the non-existence of exotic forms of matter. If exotic forms of matter do not exist (and no lab evidence suggests it does exist), the lack of LCDM to be able to "fit" the elemental composition observations of the universe without exotic matter should be used a means to falsify the LCDM model, not used as a method to try to overlook all the baryonic mass estimates that we've been making since the dawn of time.

*If* we can demonstrate the existence of exotic forms of matter via experiments on Earth, then the nucleosynthesis argument becomes valid argument IMO, but not before that point. It's an interesting "requirement" of LCDM, but nothing more IMO.
 
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  • #16
MichaelMo said:
I would be inclined to believe that the plasma mass would be concentrated closer to the core, and would thin out with distance from the core as "dark matter" halo models predict.
Hi Michael:

I am not sure I understand this. What does "plasma mass" mean here? Is it the mass of baryonic matter in a plasma state prior to the time when the universe has cooled and the state changes from plasma to gas? If so, what does "core mean? I am confused since I understood that "dark matter" halo models were about the formation of galaxies (or perhaps galactic clusters) at a time long after the plasma state of the universe.

Regards,
Buzz
 
  • #17
Hi Michael:

I looked at your first link to the 2008 paper and wondered whether that would fit with the paper from Magain, P. and Chantry, V. (2013), which I mentioned earlier in this thread, looking at Einstein rings from early galaxies and finding an error of factor of 1.8 between observed mass by luminosity and lensing mass. I thought both methods were robust and the difference due to non-radiating baryonic matter.

Adrian.
 
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  • #18
MichaelMo said:
I'll try to read through that paper this evening and I'll comment more once I've read it, but...
Hi Michael:

The following is another, and a more clearly written, discussion of the relationship between Deuterium and dark matter.
Here is a pertinent quote:
During the formation of helium nuclei, perhaps only one in 10,000 deuterons remained unpaired. An even smaller fraction fused into nuclei heavier than helium, such as lithium. (All the other familiar elements, such as carbon and oxygen, were produced much later inside stars.) The exact percentages of helium, deuterium and lithium depend on only one parameter: the ratio of protons and neutrons--particles jointly categorized as baryons--to photons. The value of this ratio, known as n (the Greek letter eta), remains essentially constant as the universe expands; because we can measure the number of photons, knowing n tells us how much matter there is. This number is important for understanding the later evolution of the universe, because it can be compared with the actual amount of matter seen in stars and gas in galaxies, as well as the larger amount of unseen dark matter.​

For the big bang to make the observed mix of light elements, n must be very small. The universe contains fewer than one baryon per billion photons. The temperature of the cosmic background radiation tells us directly the number of photons left over from the big bang; at present, there are about 411 photons per cubic centimeter of space. Hence, baryons should occur at a density of somewhat less than 0.4 per cubic meter. Although cosmologists know that n is small, estimates of its exact value currently vary by a factor of almost 10. The most precise and reliable indicators of n are the concentrations of primordial light elements, in particular deuterium. A fivefold increase in n, for example, would lead to a telltale 13-fold decrease in the amount of deuterium created.​

Regards,
Buzz
 
  • #19
Buzz Bloom said:
...Although cosmologists know that n is small, estimates of its exact value currently vary by a factor of almost 10...
Does that help? An order of magnitude range sounds like "dark matter may or may not be there".
 
  • #20
Buzz Bloom said:
Hi Michael:

The following is another, and a more clearly written, discussion of the relationship between Deuterium and dark matter.
Here is a pertinent quote:
During the formation of helium nuclei, perhaps only one in 10,000 deuterons remained unpaired. An even smaller fraction fused into nuclei heavier than helium, such as lithium. (All the other familiar elements, such as carbon and oxygen, were produced much later inside stars.) The exact percentages of helium, deuterium and lithium depend on only one parameter: the ratio of protons and neutrons--particles jointly categorized as baryons--to photons. The value of this ratio, known as n (the Greek letter eta), remains essentially constant as the universe expands; because we can measure the number of photons, knowing n tells us how much matter there is. This number is important for understanding the later evolution of the universe, because it can be compared with the actual amount of matter seen in stars and gas in galaxies, as well as the larger amount of unseen dark matter.​

For the big bang to make the observed mix of light elements, n must be very small. The universe contains fewer than one baryon per billion photons. The temperature of the cosmic background radiation tells us directly the number of photons left over from the big bang; at present, there are about 411 photons per cubic centimeter of space. Hence, baryons should occur at a density of somewhat less than 0.4 per cubic meter. Although cosmologists know that n is small, estimates of its exact value currently vary by a factor of almost 10. The most precise and reliable indicators of n are the concentrations of primordial light elements, in particular deuterium. A fivefold increase in n, for example, would lead to a telltale 13-fold decrease in the amount of deuterium created.​

Regards,
Buzz

These types of calculations are very interesting and useful, and IMO they should be used to either falsify or verify LCDM. I would say that *if* we knew from controlled laboratory experimentation that exotic forms of matter definitely exist in nature, then such a technique might be very useful in estimating the ratio of each type of matter (dark/baryonic) that might actually exist in space.

Since we have ample evidence to suggest that the baryonic mass estimates of galaxies that we've been using are seriously innaccurate, I'm hesitant to leap to any conclusion which constricts me and *obligates* me to any specific ratio of exotic matter in the universe. How do I even know for certain that exotic forms of matter even exists at all from uncontrolled observations in space and galaxy mass estimates which are not correct? If we start assuming that a very specific ratio of exotic matter to normal matter *must* exist and therefore we *assume* that exotic forms of matter *must* exist, I think it's very easy to get lost in 'dogma' and locked into a particular dogma rather than being up front about the current limits of our technology and the serious and numerous problems in our baryonic mass estimation techniques.

If exotic forms of matter do not exist in nature, then LCDM should be falsified and die by that same prediction sword if it cannot explain the elemental abundance figures without exotic 'fudge factors".

Let's take a close hard look at the various laboratory experiments over the past decade. We have literally spent billions of dollars/euros "testing" the standard particle physics model at LHC, and thus far it's performed flawlessly. We've also tested several non standard particle physics models like SUSY theory, and they've come up empty at LHC. Not a single 'sparticle" has been observed, and LHC is now operating at close to it's maximum energy state. We've also spent many millions of dollars at LUX and PandaX and Xenon100 and now Xenon1T experiments which have all tried and failed to find direct laboratory evidence for exotic forms of matter, The results to date of every single lab experiment related to exotic matter have all been all negative.

https://en.wikipedia.org/wiki/Plasma_cosmology#Alfv.C3.A9n.E2.80.93Klein_cosmology
http://www.nytimes.com/1989/02/28/science/novel-theory-challenges-the-big-bang.html?pagewanted=all

If you set aside any need for creation (of matter) concepts for a moment there is no evidence that exotic forms of matter exist. Hannes Alfven for instance proposed a cyclical type of "bang' theory that was based upon matter/antimatter interaction. His theory did not require that all matter in the universe was ever required to condense itself to a single "point' before matter/antimatter interactions began to cause it to expand again. It may have only contracted to say 10 percent of it's current size before expanding again. In such a scenario, the elemental composition of the universe today might have more to do with the original elemental composition prior to 'contraction' and less to do with with anything related to the annihilation or 'expansion' process.

A couple of other tidbits of information that may be noteworthy here are the fact that the various stellar underestimation problems which I cited earlier would tend to suggest that a significant portion of the 'missing mass' from that 2006 Bullet Cluster lensing study is likely to be found inside of stellar mass, and probably also in neutral hydrogen gas that would tend to "pass on through" a galaxy collision process. Because of various EM influences, the hot plasma halos around galaxies are more likely to "collide" in cluster collisions, but the distance between stars in any given galaxy minimize the likelihood that stars would actually physically collide very often in a 'collision' process. That type of dense matter would tend to pass right through, as would neutral atoms of dust and non plasma. The hot plasma halo tends to perform more like a "fluid" and it would be more inclined to interact and collide.

The current standard solar model predicts stellar abundance figures which are based upon the concept of 'fast" solar convection processes which presumably keep heavier elements like Nickel and Iron mixed together with wispy light elements like Hydrogen and Helium, from deep within the sun at the base of the convection zone, all the way up to the surface of the photosphere.

https://scitechdaily.com/unexpectedly-slow-plasma-flow-measured-below-the-suns-surface/

SDO measurements in 2012 revealed that contrary to 'jet speed' convection predictions of the standard solar model, SDO measured something closer to walking speed convection inside of the sun. How that "slow" convection process might affect stellar abundance figures is anyone's guess, and I would therefore hate to obligate myself to any specific elemental abundance figures at the moment.
 
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  • #21
Adrian59 said:
Hi Michael:

I looked at your first link to the 2008 paper and wondered whether that would fit with the paper from Magain, P. and Chantry, V. (2013), which I mentioned earlier in this thread, looking at Einstein rings from early galaxies and finding an error of factor of 1.8 between observed mass by luminosity and lensing mass. I thought both methods were robust and the difference due to non-radiating baryonic matter.

Adrian.

I'm falling behind on my reading at the moment but I'll try to catch up tomorrow. I'll just say at the moment that I'm comfortable with and confident in the mass calculations of galaxies that are based upon lensing techniques and galaxy rotation patterns, but I'm equally confident that our baryonic mass estimation techniques need a serious revision in light of the various discoveries of the past decade. My first instinct would be to presume that any and all 'missing mass' is likely to be found in ordinary plasma/hydrogen halos or ordinary dust, or ordinary stars rather than anything particularly exotic in nature. The two different mass halos that have been discovered (or at least better quantified) over the last five years might very well go a long way to explain our current dark matter halo models.
 
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  • #22
Buzz Bloom said:
Hi Michael:

I am not sure I understand this. What does "plasma mass" mean here? Is it the mass of baryonic matter in a plasma state prior to the time when the universe has cooled and the state changes from plasma to gas? If so, what does "core mean? I am confused since I understood that "dark matter" halo models were about the formation of galaxies (or perhaps galactic clusters) at a time long after the plasma state of the universe.

Regards,
Buzz

My reference to the term core relates to the core of galaxies. All of my comments were related to current lensing studies and/or galaxy rotation patterns *in general*, not cosmology theory per se.

Two of the references on my list were related to the discovery of both a plasma halo and a neutral hydrogen halo that surround our galaxy. Our current models of dark matter distribution would 'predict" that the stars in every galaxy are surrounded by a "halo" of mass that contains more mass than all the stars in the galaxy.

https://en.wikipedia.org/wiki/Dark_matter_halo

Indeed we find that our own galaxy is surrounded by both a halo of hot plasma, and halo of cooler neutral hydrogen atoms:

http://chandra.harvard.edu/blog/node/398
https://cosmosmagazine.com/space/galaxy-s-hydrogen-halo-hides-missing-mass

I seriously doubt that it's a coincidence that the dark matter halo models look to coincide with the mass layout patterns that we're now discovering around our own galaxy in the form of ordinary baryonic matter that we simply didn't "see/observe" until recently.
 
  • #23
stefan r said:
Does that help? An order of magnitude range sounds like "dark matter may or may not be there".
Hi stefan:

The article I quoted is relatively old, I believe it is also from the 1990s, and I believe the factor of 10 referred to the state of estimating eta before reliable astronomical measurements of Deuterium became available. There are much better estimates now, although you have pointed out that you are not satisfied that the modern values are reliable.

The quote was intended to explain the concept of the relationship between Deuterium and dark matter, and that this is an alternative way of estimating eta and from that estimating the ratio between baryonic and dark matter. Later in the article there is a discussion of improvements in the ability to measure Deuterium that had happened between the 70s and 90's.

Here is another quote I think you must gave missed.
The mere presence of deuterium sets an upper limit on n because the big bang is probably the primary source of deuterium in the universe, and later processing in stars gradually destroys it.​
This means that even before measuring how much deuterium is there, the fact that it is there at all places a lower limit on eta.

Regards,
Buzz
 
  • #24
MichaelMo said:
I seriously doubt that it's a coincidence that the dark matter halo models look to coincide with the mass layout patterns that we're now discovering around our own galaxy in the form of ordinary baryonic matter that we simply didn't "see/observe" until recently.
Hi Michael:

As I have been discussing with stefan, the estimate of the ratio of baryonic matter to all matter includes the estimate of the photon to baryon ratio, η, and the astronomical measurements of the abundance of Deuterium. This is an independent estimate from that based on the observed relationship of star velocities with their distance from a galactic core.

Regards,
Buzz
 
  • #25
MichaelMo said:
I'm frankly a little apprehensive about "assuming" the existence of exotic forms of matter only to make sure that LCDM mathematically "fits' some other completely different observation. I'd probably feel differently were it not for all the negative results from the various dark matter "tests" at LHC, LUX, PandaX, Xenon100,and even recent Xenon-1T results. As it stands, the nucleosynthesis argument seems more like a case of special pleading, only so that LCDM can be considered exempt by falsification by the non-existence of exotic forms of matter.

It appears that you don't know how historically dark matter theory came to be.

At first, astronomers and cosmologists did assume that baryonic matter is all that there is.

A few observations (in 1930-40) which claimed to maybe detect discrepancies, were ignored - which is ok, since there are _always_ some observations which find "something strange", but these may well be instrument errors or mistaken interpretation or logic of their authors.

Then Vera Rubin in 1970s worked on galaxy rotation curves and found that galaxies seem to be heavier than they should be. Her work was high-quality and was checked by other independent measurements, but still, science did not jump on dark matter bandwagon overnight. The status shifted to "hmmm, there is indeed something fishy here! Let's look at it more carefully!"

The entire 1980s were spent doing more observations, looking at several disjoing pieces of evidence, and all of them pointed quite consistently to the conclusion that baryonic mass alone is far from being enough to explain them.

Since you don't remember this long and convoluted process of history, you seem to assume everybody just happily fudges their models and observations to satisfy their preconceived notion that "dark matter exists"?
 
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  • #26
nikkkom said:
It appears that you don't know how historically dark matter theory came to be.

Actually I would argue that the reverse is true because I'm old enough to remember when the term "dark matter" didn't necessarily imply exotic forms of matter. I think it was Fritz Zwicky who first coined the term. Originally it didn't automatically imply an exotic type of matter however.

At first, astronomers and cosmologists did assume that baryonic matter is all that there is.

Sure, and they do in fact have observations and "galaxy mass estimations" that don't seem to jive. That conflict between observation and baryonic mass estimation could be related to almost anything, including errors in our baryonic mass estimates, which is likely considering the revelations of the past decade.

A few observations (in 1930-40) which claimed to maybe detect discrepancies, were ignored - which is ok, since there are _always_ some observations which find "something strange", but these may well be instrument errors or mistaken interpretation or logic of their authors.

Then Vera Rubin in 1970s worked on galaxy rotation curves and found that galaxies seem to be heavier than they should be. Her work was high-quality and was checked by other independent measurements, but still, science did not jump on dark matter bandwagon overnight. The status shifted to "hmmm, there is indeed something fishy here! Let's look at it more carefully!"

The entire 1980s were spent doing more observations, looking at several disjoing pieces of evidence, and all of them pointed quite consistently to the conclusion that baryonic mass alone is far from being enough to explain them.

Somewhere between the early 70's and 2006 the term however gradually "morphed" from being synonymous with "we don't know what that missing mass is made of", to being associated with an exotic type of matter. I don't have any doubt that there is evidence of 'missing mass' from galaxy mass estimation techniques, but I have no evidence to suggest that any of that missing mass is to be found in exotic types of matter, and in fact I have no laboratory evidence that exotic forms of matter even exist in nature.

Since you don't remember this long and convoluted process of history, you seem to assume everybody just happily fudges their models and observations to satisfy their preconceived notion that "dark matter exists"?

I think you misunderstand my position. I have no doubt that there is a 'missing mass' problem which could be related to just about anything, including serious mass estimation problems with our galaxy mass estimation models. There does seem to be *ample* evidence that we've simply been underestimating the amount of ordinary plasma that is present in various galaxies. We didn't even know about the existence of that hot plasma halo, or that cooler hydrogen halo around our own galaxy until quite recently in fact.
 
  • #27
Buzz Bloom said:
Hi Michael:

As I have been discussing with stefan, the estimate of the ratio of baryonic matter to all matter includes the estimate of the photon to baryon ratio, η, and the astronomical measurements of the abundance of Deuterium. This is an independent estimate from that based on the observed relationship of star velocities with their distance from a galactic core.

Regards,
Buzz

I realize that it's an independent estimate from lensing studies, and independent from galaxy rotation pattern studies, but as I pointed out before, the Alfven-Klein expansion model does not predict that all matter was ever as concentrated as you seem to believe. It could be that the various elemental abundance figures that we see today are in no way related to a 'big bang" event, but those ratios may simply relate back to the abundance of elements that existed *before* expansion. I can't just "assume" that A) exotic matter exists, and B) it makes up X percent of the universe based on that technique.
 
  • #28
MichaelMo said:
I think you misunderstand my position. I have no doubt that there is a 'missing mass' problem which could be related to just about anything, including serious mass estimation problems with our galaxy mass estimation models.

Ok.

There does seem to be *ample* evidence that we've simply been underestimating the amount of ordinary plasma that is present in various galaxies. We didn't even know about the existence of that hot plasma halo, or that cooler hydrogen halo around our own galaxy until quite recently in fact.

The cooler halo: you classified it as "in 2012, we 'discovered' more ordinary baryonic matter *surrounding* every galaxy that exist inside of the stars themselves", but the paper you refer to estimates it to weigh about 1.5-2% of Galaxy's mass (see my post #11 in this thread). It seems to me that you are reading too much from pop-sci descriptions, which tend to hyperbolize.
 
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  • #29
In addition to rotation curves, Bullet cluster, and nucleosynthesis, there's also the power spectrum of baryon acoustic oscillations, which so far I haven't seen mentioned in this thread - despite being the least burdened with uncertainties.
This means there are four independent data points, all suggesting the same conclusion, which is what makes DM such a strong hypothesis.
 
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  • #30
nikkkom said:
The cooler halo: you classified it as "in 2012, we 'discovered' more ordinary baryonic matter *surrounding* every galaxy that exist inside of the stars themselves", but the paper you refer to estimates it to weigh about 1.5-2% of Galaxy's mass (see my post #11 in this thread). It seems to me that you are reading too much from pop-sci descriptions, which tend to hyperbolize.

When they only have identified about 2 percent of the matter in the galaxy, finding another 2 percent is a "large change". As I pointed out, they were comparing the amount of known stellar mass to the amount of mass they found, and it was quite comparable to the known stellar mass of the galaxy. Keep in mind that this is *in addition to* all the other baryonic mass they found recently a neutral hydrogen halo surrounding the galaxy.

https://cosmosmagazine.com/space/galaxy-s-hydrogen-halo-hides-missing-mass
 
  • #31
MichaelMo said:
When they only have identified about 2 percent of the matter in the galaxy, finding another 2 percent is a "large change". As I pointed out, they were comparing the amount of known stellar mass to the amount of mass they found, and it was quite comparable to the known stellar mass of the galaxy.

You are backtracking now. You did not say "comparable", you said:
"we 'discovered' more ordinary baryonic matter *surrounding* every galaxy that exist inside of the stars themselves".

10 billion solar masses of gas claimed in the paper is not more than all stellar mass in Milky Way. It's much less.
There are different estimates of the latter, but they are all above 40 billion solar.
Example: https://arxiv.org/pdf/1102.4340.pdf estimates total stellar mass in MW to be 64+-6 billion solar.
 
  • #32
Bandersnatch said:
In addition to rotation curves, Bullet cluster, and nucleosynthesis, there's also the power spectrum of baryon acoustic oscillations, which so far I haven't seen mentioned in this thread - despite being the least burdened with uncertainties.
This means there are four independent data points, all suggesting the same conclusion, which is what makes DM such a strong hypothesis.

Let's take a close look at those four data points:

We have a Bullet Cluster study that is known to be *riddled* with baryonic mass underestimation problems.

We have galaxy mass estimation/rotation models that also suffer from the same mass halo underestimation problems as the Bullet Cluster study.

We have a potential *falsification* mechanism for LCMD theory with respect to nucleosynthesis requirements of exotic forms of matter for which we have no laboratory evidence whatsoever, even after spending billions of dollars looking for it.

Finally we have BAO estimates which also do not work *without* the need for exotic forms of matter and energy so we have two potential falsification methods for one specific cosmology theory, specifically LCDM. Both the nucleosythesis and BAO numbers seem to work out to the same ratio of exotic vs. baryonic matter which could be used as possibly *two* different remaining data points of evidence, but they could both be falsified in the absence of exotic forms of matter and we have no evidence from the lab that exotic forms of matter exist in nature.

I'd grant you two independent data points in 2017, but not 4. :)
 
  • #33
nikkkom said:
You are backtracking now.

Well, I've already admitted that my use of the term "more" was potentially a tad misleading, and that word was worth backtracking from, but you still seem to be using a single number related to their findings, whereas they actually suggested that your 10 billion solar mass estimate was just a low end starting point and the actual number could be significantly higher:

http://www.urban-astronomer.com/news-and-updates/milky-way-surrounded-by-hot-gas/

Astronomers estimate the temperature of this hot gas at between 1 and 2.5 million Kelvins, or several hundred times hotter than the surface of the Sun. It is also huge, containing a mass of gas of at least 10 billion Suns, and possibly as much as 60 billion Suns.

Emphasis mine.

You did not say "comparable", you said:
"we 'discovered' more ordinary baryonic matter *surrounding* every galaxy that exist inside of the stars themselves".

10 billion solar masses of gas claimed in the paper is not more than all stellar mass in Milky Way. It's much less.
There are different estimates of the latter, but they are all above 40 billion solar.
Example: https://arxiv.org/pdf/1102.4340.pdf estimates total stellar mass in MW to be 64+-6 billion solar.

Their top end figure is significantly higher than 40 billion solar masses (it's 60), so in theory at least my use of the term "more" could be correct, but admittedly it's an "optimistic" (and subjective) assessment on my part. If your 70 solar mass number is correct, their 60 billion solar mass top end is still very comparable to all the baryonic mass that we had found prior to 2012.
 
  • #34
MichaelMo said:
Their top end figure is significantly higher than 40 billion solar masses (it's 60), so in theory at least my use of the term "more" could be correct, but admittedly it's an "optimistic" (and subjective) assessment on my part. If your 70 solar mass number is correct, their 60 billion solar mass top end is still very comparable to all the baryonic mass that we had found prior to 2012.

Wrong. 64+-6 billion solar masses is not the estimate of all baryonic mass in Milky Way. It's estimate of _mass of stars only_. I'm sure you know that we _know_ (for at least a century) that stars are not the only baryonic mass in MW.
Total MW mass estimates are 500-800 billion.
 
  • #35
MichaelMo said:
requirements of exotic forms of matter for which we have no laboratory evidence whatsoever, even after spending billions of dollars looking for it.

Those very same experiments also fail to detect one form of matter - neutrinos - which we are 100.00% sure exist. Therefore, non-observation (so far) of dark matter is not a strong argument against it.
In fact, many theories posit that DM is nothing else than new types of neutrino (say, right-handed neutrinos with Majorana masses).
 

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