Is Dark Matter the Missing Piece in Our Cosmic Puzzle?

[Lisa!]

I want to know more about dark matter.
Please tell me:
Why do scientists think that there should be dark matter?

 

[wolram]

Try this article Lisa

http://en.wikipedia.org/wiki/Dark_matter

Dark matter
From Wikipedia, the free encyclopedia.

In cosmology, dark matter consists of elementary particles that cannot be detected by their emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. Estimates of the amount of matter in the universe, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. In addition, the existence of dark matter resolves a number of inconsistencies in the Big Bang theory, and is crucial for structure formation.

Much of the mass of the universe is believed to exist in the "dark sector". Determining the nature of this missing mass is one of the most important problems in modern cosmology. About 25% of the universe is thought to be composed of dark matter, and 70% is thought to consist of dark energy, an even stranger component distributed diffusely in space that likely cannot be thought of as ordinary particles.
Science
Unsolved problems in physics: What is dark matter? How is it generated? Is it related to supersymmetry?

The question of the existence of dark matter may seem irrelevant to our existence here on Earth. However, whether or not dark matter really exists could determine the ultimate fate of the present universe. We know the universe is now expanding because of the red shift that light from distant heavenly bodies exhibits. The amount of ordinary matter seen in the universe is not enough for gravity to stop this expansion, and so the expansion would continue forever in the absence of dark matter. In principle, enough dark matter in the universe could cause the universe's expansion to stop or even reverse (leading to an eventual Big Crunch).

 

[Garth]

And welcome to these Forums Lisa!!

Good question, keep them coming!

It may be constructive to note that there are other ideas about Dark Matter such as MOND (MOdified Newtonian Dynamics), which may be pertinent because DM has not (yet) been identified.

The problem with the standard model is that model also predicts that the baryonic density (i.e. ordinary matter, proton electrons, neutrons etc.) should only be about 4% of the critical density. Therefore, if that is correct, most of this DM (23% critical density) must be in some exotic, unknown, form.

The standard model predicts the overall density is actually the critical density so it also requires that 76% of the mass of the universe is in the form of Dark Energy. (Useful as well to make the universe accelerate in its expansion).

Thus according to that standard model not only have we not discovered 96% of the mass of the universe but also we have no idea of the form that it may be!

Some of us have suggested other models that do not require Dark Energy or non-baryonic Dark Matter at all. We shall see...

Garth

 

[Lisa!]

Thanks both of you.

Try this article Lisa

[URL]http://en.wikipedia.org/wiki/Dark_matter[/u.[/QUOTE]
I couldn't go through that.

 

[wolram]

Thanks both of you.


I couldn't go through that.

Lisa don't worry, as you read more your understanding will increase, believe
me i am a numb skull, but please read, read, read, and eventually it will not
be difficult

 

[Frank3]

I know very little about Dark Matter, but my limited reading on it seems to tell me that it (or something else) is needed to explain observed gravitational interactions in and between galaxies, and mostly distant galaxies. I don't recall seeing anything to suggest that there is a similar need to invoke Dark Matter to explain what we observe more locally, that is, to explain gravitational interactions observed in our own galaxy or solar system.

Can some one tell me about this and set me straight? That is, do we also need a Dark Matter explanation for more local observations? If so, how so (examples)? The Wikipedia site wolram gave said that the Milky Way may contain 10 times more Dark Matter than ordinary matter, but offers no observational basis for this. Do we observe the effect of Dark Matter in our own solar system or on nearby stars? If not, why not -- why would we need such a substantial factor to adjust for / explain distant observations but not need one for more local observations?

Thanks for any insights.

f3

 

[Chronos]

Hi and also welcome Lisa! Wolram and Garth did a splendid job. Permit me to add another indicator. There is a very important feature of the the universe as a whole called curvature. This curvature feature depends entirely upon the total energy content of the universe, where matter is one component of this total energy - a very dense one as expressed by e=mc^2. This total energy density tells us whether the universe will expand forever, perhaps even tearing itself apart [the big rip] or eventually stop expanding and reverse course collapsing back upon itself [the big crunch]. The term used to describe this energy density is called omega [scientists are fond of using exotic names for things to impress non-scientists]. The magic value for this omega thing, called the critical density, is 1.0000000000... If omega is less than 1.000, the universe is 'open', which means there is not enough gravity to stop the universe from expanding forever. If omega is greater than 1.000, the universe is 'closed', which means there is more than enough gravity to someday stop expansion and pull everything back together again, presumably leading to a repeat performance of the big bang. Now you probably are asking yourself, how in the world do you go about measuring this omega thing? Actually there a number of ways. Astronomers have been busily counting all of the stuff they can see [matter] in the universe and figuring how far apart they are from each other. They have also measure how much non-matter energy [radiation] is floating around in the universe. Add all of this up and you get the average measured energy density [omega] of the universe - which turns out to way less than the critical density of 1.000. Ok, then the universe is 'open' and will expand forever, right? Well, maybe not. Being diabolically clever and resourceful, scientists have also figured out how to physically measure this curvature thing. You will have to trust me on this one. It's complicated, so I will spare you the brutal details, but is quite doable as it turns out. One of the most accurate measurement made of this curvature was done with this experiment called the Wilkinson Microwave Anisotropic Probe [WMAP]. WMAP is [it's still going on] a study of the cosmic microwave background radiation [CMBR]. After analyzing the huge amount of data gathered by WMAP, scientists deduced the universe is as flat as a possum who guessed poorly at when to sprint across the interstate - omega = 1.02 ± 0.02. You can find all kinds of articles about this on the internet. Just do a search for 'WMAP omega' and you should get around 10,000 hits.

 

[Chronos]

Hi Frank3 and also welcome to PF. Truth is, there can be no more than a very small quantity of dark matter in our solar system - less than Earth mass. If there was much more than that it would, as you may suspect, mess up the planetary orbits. This would have really messed with Kepler's head when he was deriving his laws of orbital motion, as you might well imagine. Why so little of the stuff in our neighborhood yet supposedly so much in the galaxy as a whole? There is no especially good answer to that question. This is part of the reason Milgrom came up with MOND. Unfortunately, MOND doesn't answer all the hard questions either. So, as usual in the wild world of astronomy and cosmology, we have more questions than answers. The good new is, our revered elder astrophysicists have left lots of cool stuff for aspiring youngsters to discover. I have some related reading material you may find interesting:
http://www.astro.livjm.ac.uk/~ejk/dark.html
http://zebu.uoregon.edu/2004/a321/lec18.html
http://curious.astro.cornell.edu/question.php?number=571

 

[Nereid]

OK, in addition to adding my welcome to PF! to Chronos' and others', may I add my favourite spiel for DM?

The role of DM in cosmology is real ... and also hotly debated.

The role of DM in galaxies (well, actually only spirals; but that's another story) is confusing/troubling/clear/whatever ... this is the playground of MOND (also the Pioneer anomaly, and maybe more).

HOWEVER, there's another regime - not (necessarily) cosmological, and certainly not galactic - where NO ONE has come up with an even vaguely plausible alternative to DM ... rich clusters.

I've written on this numerous times - both here in PF and elsewhere - and I really don't want to repeat myself ... BUT:
a) if there is DM, then there's far, far more in the (local) universe in rich galaxy clusters than anywhere else (including the halos of spirals)
b) there are multiple, independent lines of investigation - yielding approx equal results - that the DM in rich clusters is very real, and very non-baryonic (note in passing, mostly to Garth - this is one set of good observational data which the SCC fans have yet to address, unless I have missed a key paper or three)
c) MOND explicitly cannot address this rich cluster DM (as Milgrom was among the first to fess up to)
d) the physics behind the independent 'telescopes' showing this rich cluster DM covers most of modern physics; if there's no DM, then just about ALL of modern physics is (likely) in serious trouble.

OK, enough for today.

 

[Garth]

I've written on this numerous times - both here in PF and elsewhere - and I really don't want to repeat myself ... BUT:
a) if there is DM, then there's far, far more in the (local) universe in rich galaxy clusters than anywhere else (including the halos of spirals)
b) there are multiple, independent lines of investigation - yielding approx equal results - that the DM in rich clusters is very real, and very non-baryonic (note in passing, mostly to Garth - this is one set of good observational data which the SCC fans have yet to address, unless I have missed a key paper or three)

Neried, I have followed your posts on the subject and I have been grateful for your considered criticism of baryonic DM. However, exactly why can this rich cluster DM not be baryonic?
O.K. so it is not observed, but has this ruled out all baryonic possibilities?

Garth

 

[Nereid]

Neried, I have followed your posts on the subject and I have been grateful for your considered criticism of baryonic DM. However, exactly why can this rich cluster DM not be baryonic?
O.K. so it is not observed, but has this ruled out all baryonic possibilities?

Garth,

Consider:
1) SZE: it essentially 'counts free electrons', so its estimate of mass includes all the (baryonic) plasma in the cluster, by default (unless you can construct a model which reproduces the observed effect, AND gives the same estimates of total cluster mass as hydrodynamic IGM equilibrium, Virial Theorem, and GR lensing)
2) 'distant object/quasar absorption': the lines in the spectra of background objects rule out significant quantities of neutral gas (at least, enough to account for the mass 'missing' in the 3, independent 'total mass' methods
3) colours of distant objects seen through the cluster: essentially zero 'IGM reddening', so no significant amount of 'missing baryons' in the form of dust
4) systematic errors (in observations): OK, this may have legs, but to show that the many sets of independent observations are consistent - within rigourously analysed datasets - would be quite a challenge (and AFAIK, no one has even hinted this is where the resolution may lie)
5) what does that leave us with? red or white or brown dwarfs loose in the cluster potential? pebbles and rocks? rogue Jupiters and comets?? Just to think of how there could be enough of any of these to make up the gap must give one a headache! how did they get there? where did they form? why aren't the transition objects visible (e.g. SNR, PNe)? why are the cluster galaxy stars still primarily H/He (if the missing mass is in the IGM and not primarily H/He)?
6) ultra-massive (DM?) halos for the cluster galaxies: inconsistent with lensing and X-ray observations (not to mention galaxy velocity dispersions)
7) some combination of all of the above? This would actually be rather nice! a giant, cosmic joke ... just the right balance to throw all independent sets of observations off, by just the right amounts

Note that, for sure, there is 'missing mass' in the form of plasma clumps, rocks, rogue Jupiters, white/red/brown dwarfs, neutral gas, dust, ... but no way (consistent with the observational results) that all of this added up could amount to more than a small fraction of what we estimate to 'missing' ... from three independent types of observations (just in case I didn't already say that).

Have I missed anything significant?

 

[ray b]

or in simple terms
the math doesnot work , something is missing
so we call it DARK MATTER and DARK ENERGY
so we need DARK MATTER and DARK energy to balance the books
on the univerce we see and how we think gravity "works"
just exactly what it is we have only very a few vauge clues
and a better idea on what it is not then what it is

 

[Lisa!]

Thanks all of you.

Lisa don't worry, as you read more your understanding will increase, believe
me i am a numb skull, but please read, read, read, and eventually it will not
be difficult

Oh thank you but you know it was my browser problem.I couldn't go through the link and read it at all.?(I'll give it a try again)

 

[Garth]

Garth,
........
Have I missed anything significant?

Thank you Nereid for that considered reply.

The hypothesis I wish to test is:
“The DM (23% closure density – Omega = 0.23) is primordially baryonic.”

Here there is no question as to existence of DM, especially rich cluster DM, but, ‘Have you missed anything significant?’ The first response from those holding to the standard model to my hypothesis would be, “It cannot be baryonic, because BB Nucleosynthesis only allows a baryonic 4% closure density; and that is pushing it.” (Before WMAP this value was generally thought to be limited to 2% – 3%)

However the Concordant “Freely Coasting” Cosmology model produces a baryonic closure density of 23.9% and so this cosmological objection may be overcome, the question is where is all this baryonic matter now?

You were right to question a “cosmic joke”, that is a contrived mix of just the right ingredients to mislead the set of observations that have placed a low maximum limit on observed baryons.

But first let us remember how ‘contrived’ the standard model is. Dark energy, or cosmological acceleration, has to be massively ‘switched on’ to provide inflation to overcome the horizon, flatness and smoothness problems of the Friedmann models. Next, it is ‘switched off’ during the nucleosynthesis period to produce the right ‘cosmic mix’. Then it is ‘switched back on’ to account for the distant SN Ia observations, and finally it is ‘switched back off again’ for the recent past period. The result is a model that fits the observations; but forgive me if I am a little sceptical of this scenario and see it as ‘contrived’!

Note the freely coasting model does not require inflation or non-baryonic DM, it does not require DE to explain the distant SN Ia observations but it does require a mechanism to deliver that linear expansion. SCC provides that mechanism in the form of a non-minimally connected ‘Machian’ scalar field, and furthermore it does not require significant DE to make up the closure density. The SCC model is conformally flat, yet closed, so that it not only fits the WMAP spectrum peaks but also the WMAP lack of low mode anisotropies.

The problem with the SCC model is locating the baryonic DM. This could be an irrelevant question if the theory is rubbish, however, should GPB come up trumps for SCC it may then become the most relevant astrophysical/cosmological question of all!

My scenario:
1. Out of the freely coasting BB emerges a dense plasma of H He and high metallicity.
2. A series of over-dense inhomogeneities condense into a series of objects with a ~linear log-log mass function.
3. A few super-massive BHs (10⁶ – 10⁹)M_Solar form.
4. Massive PopIII stars quickly consume their fuel and go SN. They re-ionise the IGM and leave many intermediate mass BH’s (10 – 10⁵)M_Solar.
5. Finally a dense high metal IGM permeates space.
6. The super-massive and massive BHs form the nuclei for galaxy formation, which leads to PopII star formation and further metallicity.
7. Finally PopI stars with planetary systems form. And here we are.


This ‘hand waving’ scenario would lead us to expect, together with the normal galactic and stellar systems, a high metallicity IGM (observed in the Lyman alpha forest), a number of super massive BHs (observed in galactic centres/quasars) and a huge number of intermediate mass BHs. (I am warming to Smolin’s CNS hypothesis that our universe maximises BH number!)
Could these intermediate BHs be the unobserved DM?

All I have to do is put some numbers to this! Is anyone willing to help? Does anyone think it worth discussing this further? Shall we start another thread?

Garth

 

[matt.o]

Hi Garth, one thing you need to remember is the hierarchical fromation methods involving Lambda CDM models mimick what we observe very closely. Since baryons collapse in a very different manner to CDM, it would be difficult to derive models that describe what we observe in large scale structure.

you also need to ask yourself; what would we observe if there were ~10^9 intermediate mass black holes residing in a cluster (since dark matter makes up around 10^14-10^15Msolar in a rich cluster, you would need around 10^9 to account for the unobserved mass)?

 

[turbo]

My scenario:
1. Out of the freely coasting BB emerges a dense plasma of H He and high metallicity.
2. A series of over-dense inhomogeneities condense into a series of objects with a ~linear log-log mass function.
3. A few super-massive BHs (10⁶ – 10⁹)M_Solar form.
4. Massive PopIII stars quickly consume their fuel and go SN. They re-ionise the IGM and leave many intermediate mass BH’s (10 – 10⁵)M_Solar.
5. Finally a dense high metal IGM permeates space.
6. The super-massive and massive BHs form the nuclei for galaxy formation, which leads to PopII star formation and further metallicity.
7. Finally PopI stars with planetary systems form. And here we are.

Can you supply a time-line (approximate epochs) for items 3-7? The reason I ask is that as far back as we have been able to see (z~6.5) quasars and their host galaxies exhibit metallicities similar to or higher than that of our own galaxy. There has been no observed evolution in metallicity with redshift. This is a happy circumstance for an infinite steady-state universe, but puts some constraints on the Big Bang model (galaxies of super-solar metallicity form in less than a billion years). I know that your freely coasting model gets some extra breathing room in this regard (>13.7Gy), but at what point would you regard this metallicity as a constraint on your model? If the Webb or the LBT can push these observations back to z~7, 7.5, 8, etc, with no evolution of metallicity, where do we start questioning the validity of the BB model in SCC?

 

[Garth]

Hi Garth, one thing you need to remember is the hierarchical fromation methods involving Lambda CDM models mimick what we observe very closely. Since baryons collapse in a very different manner to CDM, it would be difficult to derive models that describe what we observe in large scale structure.

you also need to ask yourself; what would we observe if there were ~10^9 intermediate mass black holes residing in a cluster (since dark matter makes up around 10^14-10^15Msolar in a rich cluster, you would need around 10^9 to account for the unobserved mass)?

Thank you matt.o Hi! Indeed what would we observe?
The SCC freely coasting model (SCC's Einstein conformal frame) has the following parameters:
R(t) = t,
Omega_baryon = 0.22 (precisely 2/9),
Omega_{false vacuum} = 0.11 (precisely 1/9),
Omega_total = 0.333 (precisely 1/3)
Has anyone run a hierarchial model simulation of these parameters? At the moment I don't feel able to re-run the programme of cosmological research for the past twenty years on my own, but I'm willing to try with help!
It would be interesting to see what it would come up with and so compare with the LambdaCDM model.

As far as observing the intermediate BH's is concerned we would need 10¹² of 10⁹ M_Solar in a rich cluster. So lensing events are to be expected. Are these observed? In our galactic halo microlensing surveys, ( Preliminary results on galactic dark matter from the complete EROS2 microlensing survey ), have shown that MACHOs (< 10² M_Solar) (based on 4 microlensing events) can account for only 3% of the halo mass. However these speculative objects could be small BHs, in which case there may exist a population of rarer, more massive, objects that would account for the greater percentage of the halo mass. Should these have been observed? Has anyone looked?

Garth

 

[Garth]

Can you supply a time-line (approximate epochs) for items 3-7? The reason I ask is that as far back as we have been able to see (z~6.5) quasars and their host galaxies exhibit metallicities similar to or higher than that of our own galaxy. There has been no observed evolution in metallicity with redshift. This is a happy circumstance for an infinite steady-state universe, but puts some constraints on the Big Bang model (galaxies of super-solar metallicity form in less than a billion years). I know that your freely coasting model gets some extra breathing room in this regard (>13.7Gy), but at what point would you regard this metallicity as a constraint on your model? If the Webb or the LBT can push these observations back to z~7, 7.5, 8, etc, with no evolution of metallicity, where do we start questioning the validity of the BB model in SCC?

Hi turbo-1 I won't engage in any more 'hand waving' in terms of putting ages to these epochs without doing the calculations. However the linearly expanding model gives considerably more breathing space in the earliest PopIII star and galaxy forming epochs.

The major point though is the “Freely Coasting” model produces high primordial metallicity:

It turns out that for baryon entropy ratio eta~
5×10⁻⁹, there would just be enough neutrons produced, after nucleosynthesis commences, to give ~ 23.9% Helium and metallicity some 10⁸ times the metallicity produced in the early universe in the standard scenario. This metallicity is of the same order of magnitude as seen in lowest metallicity objects.

The problem it has is deuterium, which has to be produced by spallation in this model. Spallation occurs anyway and contaminates the results of the standard model - but that is not often acknowledged!
So there does not seem to be a problem with high z metallicity, on the contrary such observations support this model.

Garth

 

[matt.o]

i think your numbers are slightly out, a rich cluster has a mass of around 10^14-10^15 Msolar, so 10^12 of 10^9 Msolar BH's doesn't match. But anyway, I don't think this is plausible in a cluster, since the dark matter distributions seem to be smooth in a relaxed cluster (they would not be if the DM was concentrated into BH's). I am guessing we would also observe the effects of these intra cluster BH's, due to their interaction with the other baryons (ie accretion leading to outbursts etc). I don't think observations of the x-ray emitting ICM would be so featureless in nearby relaxed clusters either.

We would also need to observe quite a number of these intermediate mass black holes at the centers of clusters. I also believe that the to form this many BH's, we would need a very biased initial distribution of density perturbations.

Please note, I have not laid pen to paper to work out most of the above, and I don't intend to (not enough hours in the day!).

 

[Nereid]

First, a general comment on how well SCC may apply to 'rich cluster DM' - it surely would be good fun to crunch the cosmological (SCC) models! However, it's at the 0-th order that I will concentrate my fire (a.k.a. sharp questions; well, I hope they'll be sharp). So, to that end, let's let the herrings (red) swim away: the ratio of baryonic to non-baryonic DM for rich clusters comes from observations, not a theory in cosmology (no matter how powerful the cosmological models are) ... you take the data from observations (of many different kinds), you plug it into your favourite Virial Theorem/hydrodynamic/GR lensing/SZE/... calculators, and out pops the answer - no cosmological parameters in these calculators! (except H₀, and the 0-th order properties of the CMBR).

Some big nuts for you to crack Garth (matt.o has already mentioned several; apologies for the repetition):

- the 'missing mass' is not in the galaxies: unless gravity is way off (and in SCC it's essentially the same as GR, to the level we're discussing, right?), we can work out the total mass within spirals from the rotation curves - SMBHs, IMBHs, and all (I'm not so sure how well constrained the total mass in ellipticals is) - and we can count the galaxies ('faint dwarf galaxies' can be estimated, and the estimates constrained, by various techniques) ... so it doesn't matter whether all the stars in all the galaxies are made of Fe, whether there are billions of rogue Jupiters, whatever

- IF the 'missing cluster mass' is in the IGM, THEN it can't be (mostly) baryonic UNLESS it's not ionized (from SZE observations) and not gas (from absorption lines) and not dust (from absorption spectra and a lack of reddening). Note that analyses of the Lyman forest - so far - are lacking in good 'smoking guns' (AFAIK, there are no Lyman system quasars 'behind' the well observed SZE/lensed/X-ray/virial-theorem-observed clusters), no doubt these will turn up in the next decade or so. HOWEVER, if you'd like to make an estimate of what the IGM plasma/gas/dust composition must be to account for (say) 80% of the 'missing cluster mass', we could then test whether that is consistent with observational data

- the IMBHs: you may be onto something here. Do you have an OOM mass distribution (if not, you could always just assume a 'reasonable' one)? If there were sufficient numbers to account for the 'missing cluster mass', and spread evenly (relatively speaking) throughout the cluster, what could we expect to see? While there's certainly some work you could do on things like their relaxation time (would they be approx virialised by now?), maybe the first cab off the rank would be things like how many should be passing through a galaxy 'now', how would they interact with the IGM, how often would they collide/merge/form binaries, how would they 'show up' in lensed clusters (and how), ...

 

[Garth]

matt.o of course, I'm having a bad hair day! I meant 10¹² of 10³ M_solar BHs. These are the intermediate BH's that are the end state of massive PopIII stars in the supposed range (10 - 10⁵) M_solar, I took 10³ M_solar as a 'typical' value.

Nereid thank you again - I appreciate that the ratio of baryonic to non-baryonic DM for rich clusters comes from observations, therefore the baryonic density is that which we can see. My proposal is that most of the rich cluster DM is invisible material (hence Dark Matter) that originally (out of the BB) was baryonic but is now in some dark bound form. IMBH would seem the obvious suggestion as we already suspect there was a period of brilliant massive PopIII stars that re-ionised the IGM at an early stage, some say twice, and these would leave IMBHs behind.

That there is some IGM gas is well accepted, and the Lyman alpha forest shows that it has high metallicity, but I'm not relying on it to supply much of the total baryonic mass. It does however require some explaining as only 20% or so can be accounted for from stellar nucleosynthesis and galactic outgassing.

Typical rich cluster size? 10⁷ parsecs diameter? Volume ~10²¹ parsecs³ IMBH density ~ one per ~10⁹ parsecs³, i.e. ~ one per 10³ parsecs in ball park numbers. Is there a IMBH within a thousand parsecs? There could well be! The numbers are not impossible.

Garth

 

[turbo]

That there is some IGM gas is well accepted, and the Lyman alpha forest shows that it has high metallicity, but I'm not relying on it to supply much of the total baryonic mass. It does however require some explaining as only 20% or so can be accounted for from stellar nucleosynthesis and galactic outgassing.

There is another viable candidate for the missing mass, although most people are probably sick of hearing me talk about it by now. It is commonly accepted by quantum physicists that the gravitational potential expressed by the energies of the vacuum field would be able to collapse the visible universe to a size smaller than the orbit of the moon, if they were not very finely balanced to about 120 OOM. I believe that this does not happen because of the Pauli exclusion principle. These virtual particle-antiparticle pairs are fermions and they resist occupying the same states as their neighbors, so there is always a dynamical balance between their gravitational attraction and their mutual repulsion. In white dwarves and neutron stars the Pauli exclusion principle provides the pressure to prevent further collapse, and I believe the same dynamical balance holds true in less-degenerate gravity realms.

 

[Mike2]

There is another viable candidate for the missing mass, although most people are probably sick of hearing me talk about it by now. It is commonly accepted by quantum physicists that the gravitational potential expressed by the energies of the vacuum field would be able to collapse the visible universe to a size smaller than the orbit of the moon, if they were not very finely balanced to about 120 OOM. I believe that this does not happen because of the Pauli exlusion principle. These virtual particle-antiparticle pairs are fermions and they resist occupying the same states as their neighbors, so there is always a dynamical balance between their gravitational attraction and their mutual repulsion. In white dwarves and neutron stars the Pauli exclusion principle provides the pressure to prevent further collapse, and I believe the same dynamical balance holds true in less-degenerate gravity realms.

Is there a way of assigning a force-distance relationship to this Pauli exclusion principle on interstellar material? Thanks.

 

[Garth]

turbo-1 note that in the SCC model 0.11 (1/9) closure density is in the form of false vacuum energy i.e. Z.P.E.. It has a equation of state
p = -rho. i.e. w = -1.

However the matter density (visible baryonic matter and DM)is twice this; Omega_m = 2/9.

Garth

 

[juju]

Hi,

It may be that both dark matter and dark energy considerations may be heandled by the appropriate modification of general relativity.

juju

 

[turbo]

Is there a way of assigning a force-distance relationship to this Pauli exclusion principle on interstellar material? Thanks.

I'm sure someone could explain this in such terms, but in non-technical terms, fermions resist being forced into the same quantum states with other fermions of similar spin. As I understand it, the Pauli exclusion principle is a balance beween the position and momentum of the fermions in accordance with the Heisenberg uncertainty principle. The more tightly compacted the fermions, the more certainly their positions are defined, and the less certainly their momentums are defined. Naively, one would expect that in a domain of very low gravitation (not very densely packed) the fermions would have well-defined energies but very poorly defined positions (broad range of possible locations). The more densely they are packed the more uncertain their momenta would become. The vacuum fields in the absence of matter will be very diffuse, and in the presence of large masses of matter, they will be densely compacted.

I'm sorry that I do not have the math skills to define the Pauli exclusion principle in terms of a force-distance relationship, but let me explain WHY I believe this to be necessary. For the gravitational energy of the vacuum fields to be exquisitely (and dynamically) fine-tuned (to 120 OOM) the forces involved must necessarily arise from the SAME field. They cannot arise from the fortuitous conspiracy of two fields, because any tiny imbalance would already have led to a disastrous collapse (or explosion) of the universe. For this reason the gravitational attraction AND the balancing repulsion must of necessity both be characteristics of the same field.

 

[Nereid]

That there is some IGM gas is well accepted, and the Lyman alpha forest shows that it has high metallicity, but I'm not relying on it to supply much of the total baryonic mass. It does however require some explaining as only 20% or so can be accounted for from stellar nucleosynthesis and galactic outgassing.

Maybe, maybe not ... an interesting topic (anyone want to start a separate thread? - what does the Lyman forest tell us? about the size and nature of the gas clouds the quasar photons went through to get to us? about their space density and proximity to galaxies and clusters?), but let's let this red finned critter swim away too.

Is there a IMBH within a thousand parsecs?

We could play around with this, within the Local Group and Milky Way ... your call Garth, to what extent would our local environment be typical of that in a rich cluster (in terms of IMBHs)?

Back to rich clusters ... what sort of footprints would a billion IMBHs leave in such a cluster? Let's start with the extent to which they would 'bulk up' the galaxies in the cluster ... if they were distributed uniformly throughout the cluster, not to any significant extent, right?

What about lensing? what would the impact parameter of a typical IMBH be? How fast would they cross our line of sight (pick a motion, any motion!)? what would the 'column density' of IMBHs be? how many would be 'in front of' the galaxies on the far side of the cluster? of background objects (esp for 'lensing clusters')?

 

[Nereid]

There is another viable candidate for the missing mass, although most people are probably sick of hearing me talk about it by now. It is commonly accepted by quantum physicists that the gravitational potential expressed by the energies of the vacuum field would be able to collapse the visible universe to a size smaller than the orbit of the moon, if they were not very finely balanced to about 120 OOM. I believe that this does not happen because of the Pauli exlusion principle. These virtual particle-antiparticle pairs are fermions and they resist occupying the same states as their neighbors, so there is always a dynamical balance between their gravitational attraction and their mutual repulsion. In white dwarves and neutron stars the Pauli exclusion principle provides the pressure to prevent further collapse, and I believe the same dynamical balance holds true in less-degenerate gravity realms.

It's potentially an interesting idea turbo-1, but until you can give us something to work with - i.e. numbers, equations, or OOM calculations - the most respectful thing we could say is something like 'nice idea, please get back to us when you can model the (apparent) missing mass in rich clusters' ... or have I missed something significant?

 

[Nereid]

It may be that both dark matter and dark energy considerations may be heandled by the appropriate modification of general relativity.

Hi juju,

Indeed, that may be so.

However, unless and until such a modification appears on the scene, bursting with numbers, equations (or just plain OOM calculations), how are we to respond to such a suggestion? (other than how I just responded to turbo-1's).

 

[SpaceTiger]

For discussion of observational constraints on black holes as dark matter, see here . Basically, the only workable regime is ~100 - 10⁴ solar masses.

 

[turbo]

Maybe, maybe not ... an interesting topic (anyone want to start a separate thread? - what does the Lyman forest tell us? about the size and nature of the gas clouds the quasar photons went through to get to us? about their space density and proximity to galaxies and clusters?), but let's let this red finned critter swim away too.

I'd be happy to explore this, Nereid. You know that I'll give you headaches with regard to gravitational redshift effects, but I look forward to the discussion.

 

[turbo]

It's potentially an interesting idea turbo-1, but until you can give us something to work with - i.e. numbers, equations, or OOM calculations - the most respectful thing we could say is something like 'nice idea, please get back to us when you can model the (apparent) missing mass in rich clusters' ... or have I missed something significant?

You may have missed somthing that I have been trying to get you to pay attention to for at least a year. For the gravitational energy of the vacuum fields to be exquisitely (and dynamically) fine-tuned (to 120 OOM) the forces involved must necessarily arise from the SAME field. They cannot arise from the fortuitous conspiracy of two fields, because any tiny imbalance would already have led to a disastrous collapse (or explosion) of the universe. For this reason the gravitational attraction AND the balancing repulsion must of necessity both be characteristics of the same field.

 

[mars2]

Lisa,
I give the website a try again,and find something in it!

In cosmology, dark matter consists of elementary particles that cannot be detected by their emitted radiation but whose presence can be inferred from gravitational effects on visible matter such as stars and galaxies. Estimates of the amount of matter in the universe, based on gravitational effects, consistently suggest that there is far more matter than is directly observable. In addition, the existence of dark matter resolves a number of inconsistencies in the Big Bang theory, and is crucial for structure formation.

Much of the mass of the universe is believed to exist in the "dark sector". Determining the nature of this missing mass is one of the most important problems in modern cosmology. About 25% of the universe is thought to be composed of dark matter, and 70% is thought to consist of dark energy, an even stranger component distributed diffusely in space that likely cannot be thought of as ordinary particles.

Unsolved problems in physics: What is dark matter? How is it generated? Is it related to supersymmetry?The question of the existence of dark matter may seem irrelevant to our existence here on Earth. However, whether or not dark matter really exists could determine the ultimate fate of the present universe. We know the universe is now expanding because of the red shift that light from distant heavenly bodies exhibits. The amount of ordinary matter seen in the universe is not enough for gravity to stop this expansion, and so the expansion would continue forever in the absence of dark matter. In principle, enough dark matter in the universe could cause the universe's expansion to stop or even reverse (leading to an eventual Big Crunch).

 

[Nereid]

I'd be happy to explore this, Nereid. You know that I'll give you headaches with regard to gravitational redshift effects, but I look forward to the discussion.

Space Tiger has already started one - maybe you could start another? Something like 'what is the interpretation of the Lyman forest in QSO spectra, according to folk like Arp, Ari Brynjolfsson (and other plasma cosmologists), the CREIL crowd, etc'?

 

[Nereid]

You may have missed somthing that I have been trying to get you to pay attention to for at least a year. For the gravitational energy of the vacuum fields to be exquisitely (and dynamically) fine-tuned (to 120 OOM) the forces involved must necessarily arise from the SAME field. They cannot arise from the fortuitous conspiracy of two fields, because any tiny imbalance would already have led to a disastrous collapse (or explosion) of the universe. For this reason the gravitational attraction AND the balancing repulsion must of necessity both be characteristics of the same field.

Sorry, it seems I wasn't clear turbo-1.

The 120 OOM is a big elephant, no doubt.

What I was asking was what - quantitatively (or even with equations without estimated parameters!) - do we have to link the ZPE (or similar) to the estimated non-baryonic DM we 'see' in rich clusters?

The answer might be something like this (I'm making this up, but I think you get the idea):
- estimating cluster mass by lensing using GR gives a number that's way too high, because {insert ZPE-related equations, or OOMs, here}
- the cluster potential that galaxies feel is subtly different from what is built into the Virial Theorem, instead of {insert Virial Theorem concepts here}, it's {insert ZPE-related equations, or OOMs here}
- [similar for analyses of X-ray observations]
- so, when ZPE-related stuff is taken into account, we see that the three independent techniques will still give consistent results (to ~15%), and that the estimated cluster masses will be shown to be ~80% smaller (than they do using non-ZPE-related analyses), bringing them in line with estimates of the baryonic mass
- note that the SZE (etc) techniques are unaffected by 'ZPE-related corrections', so estimates of baryonic mass using those techniques do not need to be adjusted.

 

[Garth]

For discussion of observational constraints on black holes as dark matter, see here . Basically, the only workable regime is ~100 - 10⁴ solar masses.

So my value of 10³M_solar would work?
In a rich cluster
10¹² of 10³M_solar, (One every ~ kiloparsec).
or
10¹³ of 10²M_solar, (One every ~ 400 parsecs).

In the galactic halo/ spiral arm we are looking for about 10¹¹M_solar DM?
Therefore 10⁸ of 10³M_solar in a ~ spherical volume radius ~100 kiloparsecs? i.e. ~ 10¹⁵ parsecs³, one per 10⁷ parsecs³, (One every ~200 parsecs).
or
one of 10²M_solar per 10⁶ parsecs³, (One every ~100 parsecs).

Is this scenario reasonable?

Garth

 

[SpaceTiger]

Is this scenario reasonable?

Observationally, it can't be ruled out. The difficulty you have is in explaining nucleosynthesis with that many baryons.

 

[Garth]

Thank you ST! (Nick?)
As you will have seen from my post #14 in this thread, I have no difficulty in explaining that many baryons if we adopt a “Freely Coasting” Cosmology, a cosmology that is demanded by Self Creation Cosmology.

So then; we have either the "Mainstream cosmology model" and unknown DM and DE or an alternative cosmological theory that does not require inflation, exotic DM or DE. The alternative theory SCC is being tested, along with GR by the Gravity Probe B experiment. We wait and see!
Exciting times!

Garth

 

[Chronos]

I think that scenario has a lot of observational evidence tilting against it, but I agree with ST - the evidence is not yet compelling. The deuterium problem has not been solved [at least to my satisfaction] in any realistic model. I am sympathetic to the spalling model, but where are the clouds of spalled deuterium?

 

[Nereid]

Garth,

I'm not quite in the same camp as SpaceTiger and Chronos (an unusual occassion, no doubt) ... I reckon a population of IMBHs sufficient to account for the large majority of the observed non-baryonic DM in rich clusters (such as the OOM calculations you provided) probably can be ruled out, observationally ... and I'd like to explore this a bit further if you don't mind.

Let's start with the various observations of the distribution of DM in rich clusters (references? you have only to ask!). These show that the (mass) density of DM is 2 or 3 OOM greater near the centre than the cluster average. What can you tell us about the microlensing of an IMBH? For example, if you have one in front of a nice fat E galaxy (e.g. a cD), what should we expect to see? Now in a rich cluster there will be a trillion or more of these ... what would be the overall lensing effect?

Looking at IMBH and their trip through the one or two cD galaxies, how many would be 'passing through' at any given time? What would be their 'collisional cross section'? What rate of supernovae would you expect (from IMBH-star collisions)? How often would the IMBH acquire a nice, shiny accretion disk? What would the lifetime of such be?

 

[turbo]

Sorry, it seems I wasn't clear turbo-1.

The 120 OOM is a big elephant, no doubt.

What I was asking was what - quantitatively (or even with equations without estimated parameters!) - do we have to link the ZPE (or similar) to the estimated non-baryonic DM we 'see' in rich clusters?

Yes, but I do not have the math skills to make the all the field calculations. To get an estimate of the gravitational energy of the polarized vacuum field one could simply give it the gravitational attraction attributed now to non-baryonic DM (perhaps less some fraction for unobserved baryonic DM).

Here come the tricky parts:
a) How does the attractive force in the polarized vacuum scale with distance? Does it fall of as a function of the square of the distance from the dominant mass? This seems problematic in light of the self-attractive self-polarizing nature of the vacuum field, and may be the root cause of the disagreement between GR and MOND on galactic scales.

b) On galactic scales, it is apparent that the GR approximation results in a mass shortfall (as expected by the rotation curves of spirals in particular). MOND is reasonably predictive on galactic scales, but does not perform as well in clusters. This leads to another part of the model that I have not yet refined to my satisfaction. If we model a polarized vacuum field surrounding an isolated elliptical, we will probably end up with a field shape that mirrors the mass distribution of the galaxy. Add a second galaxy nearby, and what happens? Where their fields overlap, they will by necessity distort as they merge, perhaps forming a field that in total looks like a large blob with a central "pinch" or some other morphological version of a dogbone. I expect that the "pinch" will be pronounced when the galaxies are relatively distant from one another and much less pronounced when they are very close, resembling an ellipsoid with very soft lobes. The virtual particle pairs near this overlap will be strongly influence by the orientation of their neighbors, and will have to come to some equilibrium irrespective of the location of the masses that generated the polarized fields.

c) OK, the determining the shape of the combined fields of two galaxies is not trivial. How now to model the shape and density of the cluster's vacuum field when there are multiple galaxies of various masses and shapes, each with its own momentum? At this point, it's clearly supercomputer time, but I imagine the final picture will look like a filamentous structure with lobes surrounding each galaxy or close grouping.

Sorry about the delay in answering you, Nereid. Your questions are good, and I wish I could be more quantitative. I've got the basics of the model pretty firmly established, but the morphology of the galactic/cluster fields gets complicated, and I have not been as diligent in thinking these through, although modeling strong cluster lensing in terms of classical optics was a prime motivation for heading down this ZPE field path in the first place.

 

[SpaceTiger]

I'm not quite in the same camp as SpaceTiger and Chronos (an unusual occassion, no doubt) ... I reckon a population of IMBHs sufficient to account for the large majority of the observed non-baryonic DM in rich clusters (such as the OOM calculations you provided) probably can be ruled out, observationally ... and I'd like to explore this a bit further if you don't mind.

I shan't discourage such an exploration, but I'm fairly certain it can't be ruled out. A professor here (Jerry Ostriker) has been trying to push his primordial black hole theory of dark matter for quite some time now and he's made us well aware of the observational constraints.

What rate of supernovae would you expect (from IMBH-star collisions)?

I may tackle some of the other problems you've posed at some point, but I'm not sure why you'd expect supernovae from such a collision.

 

[Chronos]

Primordial black holes just won't cut the mustard, IMO. Not enough background gamma radiation from what I can see. Lensing events in the galactic halo also appear to be a constraint.

 

[SpaceTiger]

Primordial black holes just won't cut the mustard, IMO. Not enough background gamma radiation from what I can see.

That limit only works for the extremely low-mass black holes, since Hawking radiation is much stronger for them. Accretion limits are much more difficult to obtain.

Lensing events in the galactic halo also appear to be a constraint.

That only works for black holes in the stellar range. MACHO couldn't constrain IMBHs as dark matter.

 

[Chronos]

Agreed. So we can rule out sub-stellar mass primoridial black holes?

 

[SpaceTiger]

So we can rule out sub-stellar mass primoridial black holes?

Unfortunately not. The gamma-ray background only rules out black holes of order 10^14-16 grams. Anything much more massive would emit an unobservable amount of Hawking radiation.

 

[Garth]

Thank you ST for those observational limitations on primordial BH's.

Garth,

I'm not quite in the same camp as SpaceTiger and Chronos (an unusual occassion, no doubt) ... I reckon a population of IMBHs sufficient to account for the large majority of the observed non-baryonic DM in rich clusters (such as the OOM calculations you provided) probably can be ruled out, observationally ... and I'd like to explore this a bit further if you don't mind.

Yes please, and those references too!

Let's start with the various observations of the distribution of DM in rich clusters (references? you have only to ask!). These show that the (mass) density of DM is 2 or 3 OOM greater near the centre than the cluster average. What can you tell us about the microlensing of an IMBH? For example, if you have one in front of a nice fat E galaxy (e.g. a cD), what should we expect to see? Now in a rich cluster there will be a trillion or more of these ... what would be the overall lensing effect?

Looking at IMBH and their trip through the one or two cD galaxies, how many would be 'passing through' at any given time? What would be their 'collisional cross section'? What rate of supernovae would you expect (from IMBH-star collisions)? How often would the IMBH acquire a nice, shiny accretion disk? What would the lifetime of such be?

Schild, Some Consequences of the Baryonic Dark Matter Population , claims to have already discovered enough microlensing from planetary sized BH's to account for the present baryonic DM, say 2% closure density(?). He also seems to be 'miffed' that his observations are not in general accepted. (Perhaps because there are similar amounts of WHIM etc.?

I am proposing that the rest of the unknown DM, say an order of magnitude greater density, is also in the form of massive stellar mass BHs 10² - BHs 10³M_solar. These, because they are much larger x10^{10 - 11} they are much rarer ~10^-10 and are consequently more difficult to detect.

Garth

 

[Mike2]

Schild, Some Consequences of the Baryonic Dark Matter Population , claims to have already discovered enough microlensing from planetary sized BH's to account for the present baryonic DM, say 2% closure density(?). He also seems to be 'miffed' that his observations are not in general accepted.

This may agree with the extra lensing effect with spiral galaxies than with other kinds, because spiral galaxies would concentrate the matter into a disk and thus have a higher probability of BH's forming.

 

[curvedlogic]

The discussion has got too technical for me, so a question in very simplistic terms.

Within my limited understanding, I have never before read of missing mass being attributed to some sort of space fabric.

I read on these forums some debate on the reality of an aether, so if such a foundation for physics should exist, why would it not be a fundamental characteristic of that stuff, to be unpacking with a very specific force of its own? Indeed it would require some defining properties, so why not an apparent mass--even when considered with a total absence of any particles whatsoever?

 

[Garth]

The discussion has got too technical for me, so a question in very simplistic terms.

Within my limited understanding, I have never before read of missing mass being attributed to some sort of space fabric.

I read on these forums some debate on the reality of an aether, so if such a foundation for physics should exist, why would it not be a fundamental characteristic of that stuff, to be unpacking with a very specific force of its own? Indeed it would require some defining properties, so why not an apparent mass--even when considered with a total absence of any particles whatsoever?

In that case you are talking about Dark Energy and not Dark Matter. Even "Within my limited understanding" you probably are talking as much sense as anyone else about that elusive subject!

Garth