Galactic Rotation... no need for dark matter.

[TooMany]

Hmm, I get the combined mass of the solar system's four gas giants as ~2.5x10^27 kg, and the Sun's mass as ~2x10^30 kg. As a rough rule of thumb, Jupiter's mass is 0.1% (10^-3) of that of the Sun.

As another rough rule of thumb, a spiral galaxy's M/L ratio, in its outer disk/halo, is ~50, which is ~5 times that in the inner disk.

I think you missed a zero -> "We would need every star to create 5000 gas giants to even get near the amount of dark matter needed!"

YMMV, of course.

You are right, the mass is much larger, but probably somewhat smaller than the amount of CDM needed because the distribution would be disk-like rather than spherical. It's hard to find such computations in the literature. Nearly everything you see assumes a distribution appropriate to collision-less particles. There are very few papers published that actually even consider the baryonic alternative explanation for rotation curves (such as Davies paper). Davies does not go into great detail about how distributions affect rotation curves. I have yet to find a paper that addresses this general issue thoroughly, which I find quite surprising considering that rotation curves are claimed as powerful evidence of the existence of CDM. Theorists certainly should ask the questions "what mass distributions of known matter can account for the rotation curves and how much matter is required for each"?

ETA: Here's an interesting calculation: if the 'missing mass' (sufficient to account for the observed rotation curves) is, indeed, in the outer disk, and in the form of (unobservable, cold) H₂, what is the metalicity of that gas, in order for there to be no observed CO? From other, independent observations what is the estimated metallicity of the ISM in outer disks? Is the metallicity required by the lack of observed CO consistent with this (assuming that spiral galaxies' 'missing mass' is in the form of cold H₂ in the outer disk)?

As stated before, I believe there is some consensus that metallicity declines with radius in galaxies. If that is incorrect, I'd appreciate a reference.

Regarding the CO issue, I recently found other reasons not to expect a constant CO ratio. There is the matter of optical depth of any dense molecular clouds that exist (essentially you only see emission from a certain depth into a dense cloud. If there are molecular clouds in the outskirts, they will most certainly be colder and than those in the star-lit parts. Second I found out that CO "sticks" (condenses?) on dust particles below temperatures of 20 K. See my recent post in No Dark Matter in our Part of the Galaxy?

[TooMany]

All the matter particles in the accelerators are either Leptons, Mesons or Baryons. Barring interactions, lifetimes are: Electrons are a charged lepton, the electron neutrino is a neutral lepton. Both are stable. The rest of the Leptons decay. The only baryon that is stable (in a free state) according to the standard model, is the proton. None of the mesons are stable. Leptons are basic particles, Baryons are composed of three quarks, mesons are composed of two quarks. As far quarks, which are basic particles, only the up quark is stable. All the others decay.

Yep, I forgot to includes electrons (and the stable antiparticles as well). Supersymmetry (a very popular theory now about three decades old) predicts a new set of more massive stable particles beyond the Standard Model. It appears that LHC has already ruled out some of the most popular versions of supersymmetry. Apparently other versions of the theory can produce even heavier partner particles, perhaps unobtainable from LHC at those masses.

I believe that "neutralinos" are the hoped for CDM particle (WIMP). I admit to knowing little about this. Is a neutralino a heavy partner of the neutrino? Does supersymmetry predict new stable charged particles? If so why haven't we seen them in nature?

[Nereid]

You are right, the mass is much larger, but probably somewhat smaller than the amount of CDM needed because the distribution would be disk-like rather than spherical.

The mass is the same, irrespective of its distribution!

This is a pretty basic result, and easily derivable from Newton's F=GmM/r²; have you forgotten it?

It's hard to find such computations in the literature. Nearly everything you see assumes a distribution appropriate to collision-less particles. There are very few papers published that actually even consider the baryonic alternative explanation for rotation curves (such as Davies paper). Davies does not go into great detail about how distributions affect rotation curves. I have yet to find a paper that addresses this general issue thoroughly, which I find quite surprising considering that rotation curves are claimed as powerful evidence of the existence of CDM. Theorists certainly should ask the questions "what mass distributions of known matter can account for the rotation curves and how much matter is required for each"?

Perhaps because it's so basic, and simple (unless you try for full GR solutions) that it's left to textbooks and (undergrad) homework assignments?

As stated before, I believe there is some consensus that metallicity declines with radius in galaxies. If that is incorrect, I'd appreciate a reference.

Did I not give you one such, just yesterday?

Never mind; after the merger I'll check ...

Regarding the CO issue, I recently found other reasons not to expect a constant CO ratio. There is the matter of optical depth of any dense molecular clouds that exist (essentially you only see emission from a certain depth into a dense cloud. If there are molecular clouds in the outskirts, they will most certainly be colder and than those in the star-lit parts. Second I found out that CO "sticks" (condenses?) on dust particles below temperatures of 20 K. See my recent post in No Dark Matter in our Part of the Galaxy?

Yeah, so?

It would seem that you have a history of not thinking this sort of thing through.

For example, if it ""sticks" (condenses?) on dust particles below temperatures of 20 K", that requires there to be lots of dust! Which means the metallicity must be quite significant (to remove so much CO), right? I mean, what is dust? Tiny bits of solid helium? Flakes of solid hydrogen?

Besides, this isn't about "a constant CO ratio", this is about an order of magnitude (or two).

I know OOM (order of magnitude) thinking isn't easy - it's certainly not intuitive - but if you can't get a simple OOM calculation to come out about right, you've really got your work cut out for you.

[TooMany]

The mass is the same, irrespective of its distribution!

This is a pretty basic result, and easily derivable from Newton's F=GmM/r²; have you forgotten it?

Perhaps because it's so basic, and simple (unless you try for full GR solutions) that it's left to textbooks and (undergrad) homework assignments?

I agree with your Newtonian equation, but the notion that mass distribution is irrelevant to rotation curves seems unfounded. A disk-like distribution will have a very differently shaped field than any spherically symmetric distribution.

Spherical distributions are very easy to analyze. Any uniform spherical shell has no internal field and can be treated as a point mass at the center of the shell outside of the shell. That is not correct for a ring or a disk.

You say that it's an undergraduate homework assignment. Could you please derive for us whatever it is that you are claiming is easily derived from Newtons law of gravity?

I'm waiting for your answer Nereid...

[Amber Robot]

Second I found out that CO "sticks" (condenses?) on dust particles below temperatures of 20 K. See my recent post in No Dark Matter in our Part of the Galaxy?

What fraction of gas phase CO is expected to "stick" to dust? Is this a significant effect?

[TooMany]

What fraction of gas phase CO is expected to "stick" to dust? Is this a significant effect?

I don't know. I haven't read the whole thesis that I found this information in. At very low temperatures gases will condense. He and H2 would be the last to condense AFAIK.

Here's the quote and link if you're interested in getting more detail.

Unfortunately, each method of tracing mass in a molecular cloud is subject to its own set of biases and uncertainties. For instance, emission from CO and its isotopologues is unsuitable for studying the denser regions of a molecular cloud because the emission is optically thick and because CO is removed from the gas phase as it sticks to dust grains below ~20 K (Langer et. al. 1989).

From: Gas and dust in Molecular Clouds: Density, Temperature and Velocity Structure (Havard PhD thesis by Scott Schnee, 2006).

No doubt it depends on the exact conditions but it is a good question as is how much dust is around in galaxies and the related efficiency of condensation. I can't search the paper due to the format. I'm not sure that he goes into more specifics from just skimming it. I may have to look for other papers. The behavior of baryonic matter is very complex and certainly not yet fully understood.

The boiling point of CO (82 K) is much higher than H2 (20 K) at atmospheric pressure.

[Reality Check]

On the question of dark matter and cold H2

Lequeux et al. (1993) have proposed that there is a substantial amount of mass in cold H2 clouds in the outer galaxy. We test this hypothesis using recent molecular line observations toward the supernova remnant Cassiopeia A. From H2CO and OH absorption and CO emission line data, the molecular clouds toward Cas A are not interacting with this supernova remnant, so are typical interstellar clouds with Av. These are clouds are in the Perseus spiral arm, approximately 10 kpc from the galactic center, that is, in the outer galaxy. Since these clouds have selected on the basis of absorption line surveys, there is no bias toward warm molecular gas as in CO emission line surveys. Comparisons with 20 resolution emission line surveys. Comparisons with 20 sec resolution emission line maps of CO are used to determine the kinetic temperature, Tk. The region sampled is approximately 16 square arcmin, much more than can ever be observed using line absorption spectra toward extragalactic sources. Of more than 15 clouds toward Cas A, only one has Tk as low as 6 K. Cold H2 makes up a mass fraction of less than 8%.

My emphasis added

[Reality Check]

From: Gas and dust in Molecular Clouds: Density, Temperature and Velocity Structure (Havard PhD thesis by Scott Schnee, 2006).

The real link should be to the cited paper from this sentence in that 144 page thesis:

You cite a sentence from a 144 page thesis () and forget to look up the reference:
Dust and gas emission in Barnard 5, Langer, W. D.; Wilson, R. W.; Goldsmith, P. F.; Beichman, C. A., Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 337, Feb. 1, 1989, p. 355-381
They conclude that "For single homogeneous clouds, (C-13)O is the best CO tracer of mass and gives the best estimate of virial mass.".
IOW the mass of a molecular clouds (including H2) has the best estimate given by the CO tracer.

Whoops - you have just indirectly cited a paper that says the CO is the best tracer of mass in molecular clouds!

[tusenfem]

There are very few papers published that actually even consider the baryonic alternative explanation for rotation curves (such as Davies paper). Davies does not go into great detail about how distributions affect rotation curves. I have yet to find a paper that addresses this general issue thoroughly, which I find quite surprising considering that rotation curves are claimed as powerful evidence of the existence of CDM. Theorists certainly should ask the questions "what mass distributions of known matter can account for the rotation curves and how much matter is required for each"?

I am sure that some of these 81 papers (selected on "CDM galaxy rotation curve" in the abstract, only peer reviewed journals) will give an explanation.

[Tensor]

That is not correct for a ring or a disk.

You say that it's an undergraduate homework assignment. Could you please derive for us whatever it is that you are claiming is easily derived from Newtons law of gravity?

I'm waiting for your answer Nereid...

You're kidding, right? Centripetal force equals gravitational force at the specific radius. mv²/r = GMm/r² Where m is the test mass rotating at radius r, with velocity v. M is the mass enclosed in r and G is Newton's gravitational constant. The equation reduces to M = rv²/G. Now, it's simply a case of dropping in the values from the observed rotation curve, to determine the mass within r. You can find it in the notes and syllabus of the undergraduate course Astro 242 Physics of Galaxies and the Universe at the University of Chicago. Of course, you need to compare the M in these equations and the M in the M/L (mass/light) calculations to show why dark matter is needed. Do you have your own link for the M/L calculations, or do want us to find that for you also?

Theorists certainly should ask the questions "what mass distributions of known matter can account for the rotation curves and how much matter is required for each"?

They have been. It just turns out you didn't, again, know the basics of the field you are so willing to criticize. Let's face it. Not knowing the material that is in the undergraduate course qualifies as not knowing the basics.

[Tensor]

Yep, I forgot to includes electrons (and the stable antiparticles as well). Supersymmetry (a very popular theory now about three decades old) predicts a new set of more massive stable particles beyond the Standard Model. It appears that LHC has already ruled out some of the most popular versions of supersymmetry. Apparently other versions of the theory can produce even heavier partner particles, perhaps unobtainable from LHC at those masses.

I believe that "neutralinos" are the hoped for CDM particle (WIMP). I admit to knowing little about this. Is a neutralino a heavy partner of the neutrino? Does supersymmetry predict new stable charged particles? If so why haven't we seen them in nature?

How about this.....I'm pretty much tired of doing your legwork and trying to find basic physics for you. Only to be told I'm wrong. You've demonstrated, quite thoroughly, some basic physics and astrophysical mistakes and misunderstandings. Soooo, I'll just sit back and I'll let you make the mistakes and just provide links to show your contentions and ideas are wrong. It may take a couple of days as I'm writing this in the middle of the night, waiting for my pain pills to kick in after my surgery. The pills will keep me rather loopy over the next 48-72 hours. They may be short periods of clarity, but I wouldn't bet on it.

[Amber Robot]

I don't know. I haven't read the whole thesis that I found this information in. At very low temperatures gases will condense.

This is important to find out. If it's only a couple of percent of the gas phase then it's not a significant effect. The quote you have from Schnee's dissertation does not quantify the effect, so it's difficult to know if we should agree with his statement.

[ngc3314]

A disk-like distribution will have a very differently shaped field than any spherically symmetric distribution.

One standard derivation on this is in the Galactic Dynamics textbook by Binney and Tremaine - they have a section on how the flattening of the mass distribution affects circular velocity. Going from spherical to an oblate spheroid with axial ratio 0.3 increases the rotation velocity by ~30% for galaxy-like mass distributions (IIRC, actually at home for the holiday so don't have the book with me). That pretty much falls within the other uncertainties on total mass determinations at this point (factoring in the evidence from continuity of velocity curves in polar rings that spiral galaxy potentials are not dramatically flattened).

[TooMany]

The real link should be to the cited paper from this sentence in that 144 page thesis:

Whoops - you have just indirectly cited a paper that says the CO is the best tracer of mass in molecular clouds!

Unfortunately, CO is in practice all astronomers have to work with in order to detect cold H2. What is the alternative? The use of CO to quantify H2 is littered with assumptions that may or may not be true. The question of how much H2 gas is there is really not settled. The question of how mass is in dense H2 objects is completely unknown in low ranges of mass in comparison with stars.

Going back to your citation in your previous post "On the question of dark matter and cold H2". Did you read the conclusion?

"In summary, the proposal by LAG, that dark matter is contained in cold H2 clouds is difficult to prove or disprove conclusively."

Have you assumed that this paper is a disproof?

Here's the problem Reality Check: practically all observations in astronomy are confounded by unknowns. Published conclusions are nearly always based on a potful of assumptions (explicit or implied) which may or may not be true. Who knows what is overlooked in this study? For example, I see no mention of what happens to CO at the very low temperatures in dense clouds in this paper. Also an assumption is made about opacity of CO. This surprised me because if it is opaque in optical depth, then not much can be said about how much gas is actually traced. It is rather like trying to estimate the extent of a thick fog bank based on you ability to see 100 yards ahead.

Another difficulty that you may be overlooking is that at very cold temperatures, it is quite possible that very dense, numerous clouds in the range of AU sizes can exist. If H2 does exist in small but dense concentrations it is even more difficult to detect because such objects are not likely to be found along a random line of site. See some of Pfenniger & Combes papers on this subject.

My overall point is not that I can prove LCDM is wrong or that DM is baryonic. My point is that we don't yet know for sure. Eventually the tools available will allow us to firmly exclude various hypothesis. In the meantime science should remain open to possibilities.

[TooMany]

I am sure that some of these 81 papers (selected on "CDM galaxy rotation curve" in the abstract, only peer reviewed journals) will give an explanation.

Are you sure? Did you read them all? I read the abstracts of the first 13. All of them address the problem of making CDM distributions fit reality. Not a single one of those address "the baryonic alternative explanation for rotation curves" although as a stretch you might argue that two or three that discuss MOND are relevant. Most are concerned with eliminating the CDM cusp problem by taking baryonic effects more seriously. Want to eliminate the cusp problem altogether? Eliminate non-baryonic matter.

[TooMany]

One standard derivation on this is in the Galactic Dynamics textbook by Binney and Tremaine - they have a section on how the flattening of the mass distribution affects circular velocity. Going from spherical to an oblate spheroid with axial ratio 0.3 increases the rotation velocity by ~30% for galaxy-like mass distributions (IIRC, actually at home for the holiday so don't have the book with me). That pretty much falls within the other uncertainties on total mass determinations at this point (factoring in the evidence from continuity of velocity curves in polar rings that spiral galaxy potentials are not dramatically flattened).

Wow, that is substantial! What if the distribution was actually disk-like and not just a mere 0.3 oblate? If I understand you correctly, you are saying that more disk-like distributions explain rotation velocities using less mass.

I haven't read much about these polar ring galaxies yet. The MW marginally qualifies I suppose as most of the satellite orbits are believed to be polar but the masses are relatively small AFAIK.

[TooMany]

How about this.....I'm pretty much tired of doing your legwork and trying to find basic physics for you. Only to be told I'm wrong. You've demonstrated, quite thoroughly, some basic physics and astrophysical mistakes and misunderstandings. Soooo, I'll just sit back and I'll let you make the mistakes and just provide links to show your contentions and ideas are wrong. It may take a couple of days as I'm writing this in the middle of the night, waiting for my pain pills to kick in after my surgery. The pills will keep me rather loopy over the next 48-72 hours. They may be short periods of clarity, but I wouldn't bet on it.

Sorry to hear about your pain and I hope your surgery went well. Rest is good. No hurry in proving me wrong!

[Reality Check]

That's correct; but we do not know whether or not such gas planets exist.

You missed the point.
We do know how many stars exist and that gas giants form in stellar systems. Therefore your "DM = gas giants" idea requires that stellar system formation generates at least 500 gas giants per star! And my "less than 1%" value is being charitable. The actual value is closer to ~0.1%. So where are your stellar systems containing ~5000 gas giants? Where are the ~5000 gas giants in the Solar System?
What is more important: Where are your citations to the science that supports these massive numbers of gas giants?

There is evidence for rogue planets but observations put their number at only ~2 per star.

Astrophysicist Takahiro Sumi of Osaka University in Japan and colleagues, who form the Microlensing Observations in Astrophysics (MOA) and the Optical Gravitational Lensing Experiment (OGLE) collaborations, carried out a study of microlensing which they published in 2011. They observed 50 million stars in our galaxy using the 1.8 meter MOA-II telescope at New Zealand's Mount John Observatory and the 1.3 meter Warsaw University Telescope at Chile's Las Campanas Observatory. They found 474 incidents of microlensing, just 10 of which were brief enough to be planets of around Jupiter's size with no associated star in the immediate vicinity. The researchers estimated from their observations that there are nearly two free-floaters for every star in our galaxy.[6][7][8] Other estimations suggest a much larger number, up to 100,000 times more free-floating planets than stars in our Milky Way. [9]

N.B. Reference 9 was published last month (preprint here) and the upper estimate of up to 100,000 per star is for tiny planets (10^-8 solar masses). The paper agrees with the ~2 per star for gas giants.

So we do know whether or not such gas planets exist. There are observed to be ~2 per star.

[Reality Check]

Unfortunately, CO is in practice all astronomers have to work with in order to detect cold H2.

What is unfortunate about this?
What is means is that they have to think carefully about all of the issues with using CO to detect H2. They even can ignore looking H2 and use CO to detact any mass!
Read what you ignored:
Dust and gas emission in Barnard 5, Langer, W. D.; Wilson, R. W.; Goldsmith, P. F.; Beichman, C. A., Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 337, Feb. 1, 1989, p. 355-381
They conclude that "For single homogeneous clouds, (C-13)O is the best CO tracer of mass and gives the best estimate of virial mass.".

Going back to your citation in your previous post "On the question of dark matter and cold H2". Did you read the conclusion?

"In summary, the proposal by LAG, that dark matter is contained in cold H2 clouds is difficult to prove or disprove conclusively."

I cited this paper as evidence against your assertion that DM = cold H2.
They state "Cold H2 makes up a mass fraction of less than 8%" thus DM is not cold H2.
The next sentence after your quote is
"From our study of coulds toiwars Cas A, the amount of mass in cold H2 clouds is not sufficient to provide the dark matter deduced from galaxy rotation curves. A population of cold, very metal poor, HI poor, H2 clouds has been proposed by Pfenniger & Combes (1994); it seems that radio astromical mocular line observations cannot be used to detect such objects"
What we have is a idea from Pfenniger & Combes. It was a good idea because in 1994 there was not much evidence that DM is non-baryonic. Now any idea for DM has to explain that evidence. It is this that basically excludes H2 or sub-stellar objects as DM candidates.

Here's the problem Reality Check: practically all observations in astronomy are confounded by unknowns.

Here's the problem TooMany: You seem to think that an observation that is "confounded by unknowns" is itself unknown. Scientists know that an observation that is "confounded by unknowns" is known within error limits.

My point is that we don't yet know for sure. Eventually the tools available will allow us to firmly exclude various hypothesis. In the meantime science should remain open to possibilities.

My point is that that we don't yet know for sure but we know a lot, e.g. DM exists and the evidence is that it is non-baryonic matter. Eventually the tools available will allow us to firmly exclude various hypothesis. In the meantime science should and is remain open to possibilities.

[TooMany]

What is unfortunate about this?
What is means is that they have to think carefully about all of the issues with using CO to detect H2. They even can ignore looking H2 and use CO to detact any mass!
Read what you ignored:
Dust and gas emission in Barnard 5, Langer, W. D.; Wilson, R. W.; Goldsmith, P. F.; Beichman, C. A., Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 337, Feb. 1, 1989, p. 355-381
They conclude that "For single homogeneous clouds, (C-13)O is the best CO tracer of mass and gives the best estimate of virial mass.".

I don't understand why you think I "ignore" things. I read the entire paper. It's quite old now so it would be interesting to know how it's conclusions have held up over the years. One thing I found interesting is that C120 emissions tend to be optically thick, so are not good tracers. The paper concludes that C13O is a better tracer because they argue that it is not optically thick. However, the line is much dimmer than the much more common C12O emission. I wonder if the C13O emission can be widely used in extra galactic studies where we have a better overall view than we have of our own Galaxy.

Another interesting thing is the apparent large variation in the distribution of the isotopic forms of CO with C12, C13 and C18. It is surprising to me that such variations in mass of the same chemical compound so profoundly affect distributions.

The thrust of the paper is the suggestion that infrared dust emission can be used as a cloud mass tracer. This is suggested without discussion (that I saw) of reasons to believe that dust and gas should stay in some direct proportion.

Another interesting aspect of the paper is how it highlights the difficulty in interpreting CO measurements. There is a lot of guess work, which they do in fact try to justify at each step. Not only various assumptions that allow them measure the CO itself but also the assumptions involved in estimating the cloud mass using a virial assumption.

Nothing here allows a direct measurement of H2 mass. The indirect measurement of H2 is very complicated and depends on the assumptions. It is not unusual in the paper to mention an assumption which may change the result by a factor of 6 or more.

Here's the problem TooMany: You seem to think that an observation that is "confounded by unknowns" is itself unknown. Scientists know that an observation that is "confounded by unknowns" is known within error limits.

Count how many times the phrase "we feel" appears in this paper and then ask yourself about how confident the authors can be in drawing accurate conclusions.

My point is that that we don't yet know for sure but we know a lot, e.g. DM exists and the evidence is that it is non-baryonic matter. Eventually the tools available will allow us to firmly exclude various hypothesis. In the meantime science should and is remain open to possibilities.

I do agree that most astronomer believe that DM is non-baryonic and that only a small minority suggest otherwise and that there are reasons for this. Particularly that the DM must be non-baryonic for the BBT to work. I heartily agree that we should remain open to possibilities.

[TooMany]

There is evidence for rogue planets but observations put their number at only ~2 per star.

N.B. Reference 9 was published last month (preprint here) and the upper estimate of up to 100,000 per star is for tiny planets (10^-8 solar masses). The paper agrees with the ~2 per star for gas giants.

So we do know whether or not such gas planets exist. There are observed to be ~2 per star.

It was only a short while ago that the discovery of these "nomad" planets was a surprise. The paper you mention only has evidence for the Jupiter sized objects. From there it speculates on the rest of the distribution with little direct evidence. It's interesting that there seems to be an assumption that these kinds of objects form only in the context of star formation. I don't know the reasons for that belief. Perhaps it is simply that we know such objects are found orbiting stars.

You are misrepresenting the paper by saying that the "estimate of 10^5 per star is for tiny planets (10^-8 solar masses)". What the paper actually states is:

We have estimated that there may be up to about 10^5 compact objects per main sequence star in the Galaxy that are greater than the mass of Pluto [10^-8 solar mass].

So are they guessing that a typical main sequence star looses 10^5 planets more massive than Pluto when it forms?

[parejkoj]

It was only a short while ago that the discovery of these "nomad" planets was a surprise. The paper you mention only has evidence for the Jupiter sized objects. From there it speculates on the rest of the distribution with little direct evidence. It's interesting that there seems to be an assumption that these kinds of objects form only in the context of star formation. I don't know the reasons for that belief. Perhaps it is simply that we know such objects are found orbiting stars.

Among the other things that you don't know anything about, perhaps you should add "how gas clouds collapse" to your list.

I think you would be well served if you stopped reading papers, and started at a more basic level, like Carroll & Ostlie, or, if you're feeling adventurous, Binney & Merrifield.

So are they guessing that a typical main sequence star looses 10^5 planets more massive than Pluto when it forms?

Let's assume that's true. Would that provide enough "dark matter" to account for observed spiral rotation curves? If not, how much more would be needed?

[TooMany]

Among the other things that you don't know anything about, perhaps you should add "how gas clouds collapse" to your list.

I think you would be well served if you stopped reading papers, and started at a more basic level, like Carroll & Ostlie, or, if you're feeling adventurous, Binney & Merrifield.

I guess you suggesting that these texts prove that planetary mass objects cannot form (independently of stellar accretion disks)?

Do you mean "Introduction to Modern Astrophysics"? Do you have the 2nd edition? And "Galactic Astronomy"? There is a second edition with a different co-author. Do you have that edition?

Let's assume that's true. Would that provide enough "dark matter" to account for observed spiral rotation curves? If not, how much more would be needed?

That would depend 1) on the mass-object distribution (which I agree from current results seems unlikely to be sufficiently top-heavy) and 2) the affect of environment on the mass-object distributions (what happens in more remote and colder environments) and 3) the volume distribution of the objects within the galactic disk.

[Reality Check]

Nothing here allows a direct measurement of H2 mass.

You miss the point yet again. The paper's conclusion ius that CO is a good tracer of the mass of molecular clouds. That includes H2. There is no need to measure the mass of H2 or the mass of H or the mass of He or the mass of Be or the mass of Li or the mass of C or the mass of O + etc.

Count how many times the phrase "we feel" appears in this paper and then ask yourself about how confident the authors can be in drawing accurate conclusions.

Semantics will not help you here.

Read the abstract (where is the "we feel"?)

The relationships among IR emission, CO isotope intensities, and visual extinction in the molecular cloud Barnard 5 are studied in order to evaluate various candidates as mass tracers or molecular material and to determine the properties of dust grains emitting at 60 and 100 microns. The results establish a strong correlation between the 100 micron dust opacity and the (C-13)O column density. This relationship should allow for tracing the molecular gas with the 100 and 60 micron emission in regions without strong embedded heat sources. For single homogeneous clouds, (C-13)O is the best CO tracer of mass and gives the best estimate of virial mass. The mass of B5 estimated from the (C-13)O luminosity is 930 solar masses, while that of the core and dense fragments is only 200 solar masses. An algorithm is developed for calculating the virial mass of a cloud based on observation of optically thin lines.

[TooMany]

Read the abstract (where is the "we feel"?)

Read the paper.

[Reality Check]

The paper you mention only has evidence for the Jupiter sized objects.

You are the one talking about gas giants (e.g. Jupiter). Whay are you surprised when I cite a paper that usues observations to resitrict the numer of rogue gas giants to less than 2 per star?
This is ~0.4% of the stellar mass.
This paper debunks your idea that DM is gas giants.

You are misrepresenting the paper by saying that the "estimate of 10^5 per star is for tiny planets (10^-8 solar masses)". What the paper actually states is:

We have estimated that there may be up to about 10^5 compact objects per main sequence star in the Galaxy that are greater than the mass of Pluto [10^-8 solar mass].

Yes there may be up to about 10^5 compact objects per main sequence star in the Galaxy that are greater than the mass of Pluto.
But look at figure 1:
* The more mass per compact object the fewer they are.
* The 100,000 limit has a very sensitive dependance on a parameter.

So are they guessing that a typical main sequence star looses 10^5 planets more massive than Pluto when it forms?

Not quite - they are saying that some unknown process means that there can be up to about 10^5 compact objects per main sequence star in the Galaxy that are greater than the mass of Pluto.

However, the origin of these objects is uncertain; they may have formed directly in the collapse of the molecular cloud (Rees 1976), or have been ejected from their birth-place around a host star via a dynamical interaction(Boss 2000).
...
Though their existence is established, the origin of these unbound objects is far from clear. Do they form a continuation of the low end brown dwarf mass function near the deuterium burning mass limit, or did they form as a distinct population of objects ejected from their original host stars?

This is ~0.1% of the stellar mass.
This paper debunks anyone's idea that DM is compact objects the mass of Plutos or greater.

So we are left with "rocks" (sub-Pluto objects) but astronomers do not think that DM is sub-Pluto objects. Back of the envolope calculations show that the density of rocks needed for local DM means that they will collide within astronomically short times, making more of them that will colide even more frequently until you end up with detectable dust.
Also note that the mass function (as in the paper) means that while there are more objects as you go to lower masses, the total mass of these objects remains a tiny % of the stellar mass. 0.4% for gas giants, 0.1% for moons (Plutos), impliing a similar tiny % for asteroids.

[Reality Check]

Read the paper.

I have.
The paper's conclusion is that CO is a good tracer of the mass of molecular clouds. That includes H2.

[TooMany]

You are the one talking about gas giants (e.g. Jupiter). Whay are you surprised when I cite a paper that usues observations to resitrict the numer of rogue gas giants to less than 2 per star?
This is ~0.4% of the stellar mass.
This paper debunks your idea that DM is gas giants.


Yes there may be up to about 10^5 compact objects per main sequence star in the Galaxy that are greater than the mass of Pluto.
But look at figure 1:
* The more mass per compact object the fewer they are.
* The 100,000 limit has a very sensitive dependance on a parameter.


Not quite - they are saying that some unknown process means that there can be up to about 10^5 compact objects per main sequence star in the Galaxy that are greater than the mass of Pluto.


This is ~0.1% of the stellar mass.
This paper debunks anyone's idea that DM is compact objects the mass of Plutos or greater.

So we are left with "rocks" (sub-Pluto objects) but astronomers do not think that DM is sub-Pluto objects. Back of the envolope calculations show that the density of rocks needed for local DM means that they will collide within astronomically short times, making more of them that will colide even more frequently until you end up with detectable dust.
Also note that the mass function (as in the paper) means that while there are more objects as you go to lower masses, the total mass of these objects remains a tiny % of the stellar mass. 0.4% for gas giants, 0.1% for moons (Plutos), impliing a similar tiny % for asteroids.

I addressed this collision issue. The problem is how long can you sustain collisions? Should all asteroids be powder now?

[Reality Check]

I addressed this collision issue. The problem is how long can you sustain collisions? Should all asteroids be powder now?

No you did not address the collision issue. You made an unsupported assertion.
You can sustain collisions forever (until there is only dust and plasmna which of course can still collide!) .
Asteroids for example collide (they have impact craters).

The observational evidence remains that there is not enough mass in rocks to explain DM (solar systems do not contain enough rocks, no evidence of rocks in interstellar space).
The mass functions proposed for planetary bodies imply that there is not enough mass in to explain DM.

There is strong evidence that DM is mostly non-baryonic matter. Your idea that DM is rocks means that something keeps this non-baryonic DM out of galaxy halos. What could that be, TooMany?

ETA:
Where are these rocks in the Solar System, TooMany?
We have lots of telescopes looking for asteroids and yet they have missed these objects. We have lots of planets and moons that collect impact craters - any sign of additional bombardment from these objects, TooMany?
How does the collision frequency of your proposed rocks match with collisions with Earth, e.g. how many planet busters per million years?

P.S. for other posters, a back of the envelope calculation for the frequency of collisions was done by by a poster in the JREF forum:
JREF Post by ben m on 13th November 2009

I went ahead and did a calculation: how collisionless would "rocky" dark matter be?
...
That calculation is done for the Earth's "local" dark matter: isotropic 220 km/s orbits through a 0.3 GeV/cm^3 mean density. I gave it 5g/cm^3 density, somewhere between stone and iron.

Look at those numbers. If you built the Milky Way using Volkswagen-sized rocks as the dark matter, they'd last four thousand years between collisions; they'd be dust and plasma. Use 500 m asteroids, they'd last a million years before colliding and pulverizing. (Remember, these are 220 km/s collisions; they make Shoemaker-Levy look wimpy.) A 10^6 m planetoid could last for a gigayear---at least that survives a full Galactic orbit!---but at that point we're into the stuff that the EROS surveys have ruled out. Sub-meter-scale dust, of course, is not collisionless at all which is why it's never been even in the ballpark of viable dark matter candidates.

His assumptions may be inexact but TooMany just keeps asserting that the assumptions make the calculation wrong without actually doing the correct calculation! This sounds like an argument from incredulity or maybe ignorance.
The frequency of collisions is large for a rocky DM primarily because of the high speed of the rocks (the assumption is that they have speeds comparable to the Sun's orbital velocity of 220 km/s)..

[Shaula]

I guess you suggesting that these texts prove that planetary mass objects cannot form (independently of stellar accretion disks)?

Jeans Instability
So they cannot form by direct collapse. Which means you need some strange accretion or other mechanism, which in turn requires huge amounts of time to produce enough objects.

In short you have replaced CDM which is one unknown particle which behaves according to known laws with magic baryonic matter which has to have abnormal elemental composition, form in a completely different way to most other objects, form in such a way as to form objects of just the right size, end up in the right place in the galaxy by another unknown mechanism, somehow stay confined to the galaxy and somehow form early enough to be seen in distant galaxies.