Is Dark Matter the Missing Piece in Our Cosmic Puzzle?

[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

 

[ohwilleke]

This paper summing up dark matter evidence http://lanl.arxiv.org/PS_cache/astro-ph/pdf/0408/0408359.pdf while upbeat, does seem in my view to pose numerous serious difficulties with the theory at subcosmological scales and into terms of nucleosynthesis.